UPS Battery replacement help

[silkstone]

Hi All,

I need some advice regarding a battery replacement for my APC BX1100LI-MS UPS.

On the specifications page, it says it only uses 1x APC RBC 17 battery

All the specs on this battery line up with the UPS unit, apart from the weight which is listed at 2.6 kg for the battery, but 9.2 kg for the UPS unit, which would indicate that there are 2 batteries in there.

I also found this video of a similar unit, which shows 2 battery units in series:

My question is basically, how many batteries do I actually need to buy for this unit?

I found a shop locally selling the correct battery units: http://tanduylinh.com/index.php?mode=pro&idsp=864

But they are sold in units of 1. Now I am totally confused as to whether I just need to order 1 RBC 17 or 2 of them. Does anyone here have experience ordering and replacing batteries for UPS units?

 

[Steevo]

I have, take it apart and see is the easiest way to know.

 

[silkstone]

I have, take it apart and see is the easiest way to know.

I will, if I can't get any answers first. I've already ordered a replacement, but I'd like to use this one on my server. It just needs a battery replacement.
I'd go to a shop to have it done, but the usual battery type they replace with has a life-span of 6 months

The thing is, if I order the RBC 17, I don't know whether it will come as a single unit or 2 units joined together as 1.

 

[sneekypeet]

I'm guessing your "two in series" is correct. Unit in video looks like the same unit.

 

[Bill_Bright]

I've already ordered a replacement

Well, then a little late to ask how many cells are in that battery.

I do hope you did not buy an actual APC replacement. If you did, you paid way more than you need. I never, as in NEVER EVER buy my replacement UPS batteries from the UPS maker (and I have 8 UPS in this house, 1 on each computer, 1 on my home theater setup, and even one on my garage door opener). I typically buy my batteries on-line from Apex, BatteryWholesale, Battery Mart, Batteryplex or RefurbUPS, or Amazon depending on who has the best price on that day. Be sure to factor in shipping, which can be significant. Note prices change daily so today the price of the battery may go up but will have free shipping. Tomorrow the price may go down, but now they add in shipping charges.

Note that terminology for these SLA (sealed lead-acic) batteries are a bit confusing, until you get it sorted out.

And it does not help that APC uses there own terminology, instead of the industry standards.

The APC RPC17 is really a "12V 9Ah F2" battery. That means it is 12 VDC, 9 amp-hours and it has F2 type terminal connectors.

The APC RPC17 is a single cell battery as seen here. You should only need one cell but as Steevo suggested, it is best to open it up and check before ordering. This is especially true since UPS makers, and especially APC, make several models of UPS. These are all APC 1100 UPS.

Note the price of that RPC17 - that's expensive! And that does not even including shipping! If you shop around, you can find the same battery for much less - as seen here - with free shipping!

Now obviously, prices will be different in Vietnam so you will need to shop around.

Also, do not just toss the old battery in the trash bin. In the US, Best Buy will take in old batteries for proper recycling. I recommend you look around for recycling centers in your region.

****

As for terminology - batteries are made up of cells. As noted it looks like your battery is a single cell battery. But many UPS use 2, 3, 4 or even more cells to make one battery. If yours really is one cell, then connecting the wires to the UPS electronics will be no problem. A two-cell battery typically is pretty straight forward too. But when you start getting into batteries that have 3 and 4 cells, they typically are strapped in some type of series-parallel configuration to keep the total output voltage at either 6 or 12V. They typically will use small jumper cables. Keep those! And document how the battery is connected to the UPS electronics and how the cells are strapped together to form the whole battery. A picture is worth a 1000 words.

UPS SLA batteries typically come with either F1 or F2 terminals. Adapters are available but typically the battery compartments in UPS are very confined spaces and there may be little to no room for an adapter. So it is best to make sure you buy the right type from the start. They look very similar, but as seen here, the F2 terminal is wider.

 

[John Naylor]

I used to get all mine for free froma contractor friend ... who replaced them for a Fortune 500 company on a 2 year interval.... id normally get another 3 years outta them. But Replacements often will have higher AM options.

Do check the dimensions, voltage, ampere hours and connections.

I'm on my 4th laptop battery... bought an extra when I purchased for extended usage needs ... 1st replacement I got from laptop supplier. The ;latest replacement, he said "we don't stock them anymore, we buy from Amazon and he gave me a link... was same battery OEM but higher AH rating. Since then I been UPS batteries using Amazon. Price is the same or less, AH rating was again higher than origianl (like usual suspects) but Amazon delivered next day and manufacturer provided a full 3 year warranty ... all the usually sources were 2.

 

[Bill_Bright]

Laptop batteries use a totally different technology (lead acid vs Lithium Ion) and there are a totally different issue and totally irrelevant to this topic for many many reasons.

UPS use industry standard "SLA" 6 or 12V batteries. Laptop batteries are always proprietary and of course, are typically Li-Ion and come in all sorts of different voltages, shapes and sizes.

As for Amp hour ratings being higher, that is not a problem. You can always go higher there but not lower. It is the voltage that must be the same. FTR, several of my UPS came with 12V7Ah batteries. When time came to replace them, I put 12V9Ah cells in there. The advantage is significantly longer run times.

 

[silkstone]

Well, then a little late to ask how many cells are in that battery.

I do hope you did not buy an actual APC replacement. If you did, you paid way more than you need. I never, as in NEVER EVER buy my replacement UPS batteries from the UPS maker (and I have 8 UPS in this house, 1 on each computer, 1 on my home theater setup, and even one on my garage door opener). I typically buy my batteries on-line from Apex, BatteryWholesale, Battery Mart, Batteryplex or RefurbUPS, or Amazon depending on who has the best price on that day. Be sure to factor in shipping, which can be significant. Note prices change daily so today the price of the battery may go up but will have free shipping. Tomorrow the price may go down, but now they add in shipping charges.

Note that terminology for these SLA (sealed lead-acic) batteries are a bit confusing, until you get it sorted out.

And it does not help that APC uses there own terminology, instead of the industry standards.

The APC RPC17 is really a "12V 9Ah F2" battery. That means it is 12 VDC, 9 amp-hours and it has F2 type terminal connectors.

The APC RPC17 is a single cell battery as seen here. You should only need one cell but as Steevo suggested, it is best to open it up and check before ordering. This is especially true since UPS makers, and especially APC, make several models of UPS. These are all APC 1100 UPS.

Note the price of that RPC17 - that's expensive! And that does not even including shipping! If you shop around, you can find the same battery for much less - as seen here - with free shipping!

Now obviously, prices will be different in Vietnam so you will need to shop around.

Also, do not just toss the old battery in the trash bin. In the US, Best Buy will take in old batteries for proper recycling. I recommend you look around for recycling centers in your region.

****

As for terminology - batteries are made up of cells. As noted it looks like your battery is a single cell battery. But many UPS use 2, 3, 4 or even more cells to make one battery. If yours really is one cell, then connecting the wires to the UPS electronics will be no problem. A two-cell battery typically is pretty straight forward too. But when you start getting into batteries that have 3 and 4 cells, they typically are strapped in some type of series-parallel configuration to keep the total output voltage at either 6 or 12V. They typically will use small jumper cables. Keep those! And document how the battery is connected to the UPS electronics and how the cells are strapped together to form the whole battery. A picture is worth a 1000 words.

UPS SLA batteries typically come with either F1 or F2 terminals. Adapters are available but typically the battery compartments in UPS are very confined spaces and there may be little to no room for an adapter. So it is best to make sure you buy the right type from the start. They look very similar, but as seen here, the F2 terminal is wider.

I mean that I've ordered a replacement UPS unit for my PC. I'm going to replace the batteries in my current one and re-use it with my home server.

I'm looking at manufacturer original batteries as they come with a 1 year warranty and I know they'll be good quality. Unfortunately, most replacements here are Chinese crap.
I took a 600VA UPS in to have the battery replaced, but the replacement only lasted a few months and it cost the same as a just buying an original battery.

I've found the RPC 17 for about $20 each, I figure that 2 of them is still only 1/2 the price of a new unit. Looking again at the specs of the unit, I figure it must take 2. There's no way it can weigh 10 kg with only 2.5kg for the battery.

 

[newtekie1]

I've found the RPC 17 for about $20 each, I figure that 2 of them is still only 1/2 the price of a new unit. Looking again at the specs of the unit, I figure it must take 2. There's no way it can weigh 10 kg with only 2.5kg for the battery.

I believe it. Those transformers are heavy as hell.

I'm betting it only takes one, the 1400VA model takes the APCRBC113, which is two RBC17 batteries.

 

[silkstone]

I believe it. Those transformers are heavy as hell.

I'm betting it only takes one, the 1400VA model takes the APCRBC113, which is two RBC17 batteries.

Looks like I'm going to have to crack that sucker open to check.

It seems that I can actually use better batteries inside, but apart from going through all the specs for each battery type, I don't think there's another way to find compatibility.

 

[newtekie1]

Looks like I'm going to have to crack that sucker open to check.

It seems that I can actually use better batteries inside, but apart from going through all the specs for each battery type, I don't think there's another way to find compatibility.

UPSes don't really care much about what battery you put in them as long as they are the correct voltage. I've seen units modified with cables running out of them connected to full on car batteries. The only spec that matters is voltage, and most of them either take 12v or 24v(two 12v in series). You obviously have to worry about size too if you want the battery to still be inside the unit. But all the other specs don't really matter, just voltage and maybe size.

 

[Bill_Bright]

I'm looking at manufacturer original batteries as they come with a 1 year warranty and I know they'll be good quality. Unfortunately, most replacements here are Chinese crap.

Sorry but all three of those reasons are based on flawed assumptions.

1. The batteries from all the links I provided come with a 1 year warranty.​

2. They are all quality batteries.​

3. APC does not make their own batteries - they buy them from China. In fact, if you peal off the APC label (and yes, I have) you typically will find one of these.​

Please note I doubt you will find a stronger proponent for UPS on this forum than me! I always recommend all computers be supported by a "good" UPS with AVR since surge and spike protectors are little more than fancy and expensive extension cords.

I have been using UPSs on my sensitive electronics for decades. In fact, my oldest UPS is an APC Smart-UPS 900 that is over 25 years old. It is currently supporting my garage door opener. You can tell it is old by the color (which is why it is in the garage, BTW). I have had to replace the batteries 4 times over the years and have never once bought the replacements from APC. I have never had any replacement battery fail before 4 years. Typically, depending on how they are used, all UPS batteries need to be replaced every 3 - 5 years.

If you buy your replacements from APC, you do NOT get a longer warranty nor do you get better quality cells. What you get is ripped off with higher prices. Yes, you will get quality cells from APC, but there is no reason to assume you will not get equal (or even better!) quality from one of those 3rd party suppliers. And again, you still get a 1 year warranty - all for much less money.

It seems that I can actually use better batteries inside, but apart from going through all the specs for each battery type, I don't think there's another way to find compatibility.

Again, "better" batteries? That's not an issue. And since that UPS already comes with 12V9Ah batteries, it is not likely you will be able to put in higher capacity cells either. This is because 9Ah cells are typically the highest capacities used in UPS (until you start getting into very big commercial units). There are 12V11Ah cells for example, but they typically are physically larger and will not fit inside the UPS battery compartment. Or their terminals are of a different type and oriented differently too as seen in this example.

But all the other specs don't really matter, just voltage and maybe size.

Almost true. As I said above, when it comes to the amp-hour specification, you can always go higher (which is why car batteries will work) but you cannot go lower. If your UPS calls for 12V9Ah batteries and you install 12V7Ah, there's a good chance the UPS will simply shut down during a power outage due to the load on the batteries from all the connected devices being too big. Also, the terminal types may matter too.

 

[silkstone]

Sorry but all three of those reasons are based on flawed assumptions.

1. The batteries from all the links I provided come with a 1 year warranty.​

2. They are all quality batteries.​

3. APC does not make their own batteries - they buy them from China. In fact, if you peal off the APC label (and yes, I have) you typically will find one of these.​

Please note I doubt you will find a stronger proponent for UPS on this forum than me! I always recommend all computers be supported by a "good" UPS with AVR since surge and spike protectors are little more than fancy and expensive extension cords.

I have been using UPSs on my sensitive electronics for decades. In fact, my oldest UPS is an APC Smart-UPS 900 that is over 25 years old. It is currently supporting my garage door opener. You can tell it is old by the color (which is why it is in the garage, BTW). I have had to replace the batteries 4 times over the years and have never once bought the replacements from APC. I have never had any replacement battery fail before 4 years. Typically, depending on how they are used, all UPS batteries need to be replaced every 3 - 5 years.

If you buy your replacements from APC, you do NOT get a longer warranty nor do you get better quality cells. What you get is ripped off with higher prices. Yes, you will get quality cells from APC, but there is no reason to assume you will not get equal (or even better!) quality from one of those 3rd party suppliers. And again, you still get a 1 year warranty - all for much less money.
Again, "better" batteries? That's not an issue. And since that UPS already comes with 12V9Ah batteries, it is not likely you will be able to put in higher capacity cells either. This is because 9Ah cells are typically the highest capacities used in UPS (until you start getting into very big commercial units). There are 12V11Ah cells for example, but they typically are physically larger and will not fit inside the UPS battery compartment. Or their terminals are of a different type and oriented differently too as seen in this example.
Almost true. As I said above, when it comes to the amp-hour specification, you can always go higher (which is why car batteries will work) but you cannot go lower. If your UPS calls for 12V9Ah batteries and you install 12V7Ah, there's a good chance the UPS will simply shut down during a power outage due to the load on the batteries from all the connected devices being too big. Also, the terminal types may matter too.

Thanks for the extra info Bill. I'm not in the US or EU, so finding quality batteries is really problematic (Even for my motorbike, it difficult to get good quality Lead Acid Batteries). The one you linked is actually the same price as the APC one that I have found ($25) with shipping.
I will have a look around some more though, but the APC ones are not that much over the cost of other ones I've come across, that typically only come with 6-months warranty. I also know they'll fit.
I do need to look for a new battery for my 600VA UPS too, so I may try a cheaper one for this. I can't find an original RBC 125 anyway.

 

[Bill_Bright]

If you can find an APC replacement for the same price, then go for it. If the battery consists of more than one cell, the APC version will likely come with the cells taped together and already properly strapped - one less thing to worry about.

 

[John Naylor]

Laptop batteries use a totally different technology (lead acid vs Lithium Ion) and there are a totally different issue and totally irrelevant to this topic for many many reasons.

Ummm... no. Before you jump to criticize read all the words in the post .... especially the part that says:

"Since then I been ***UPS batteries**** using Amazon. Price is the same or less, AH rating was again higher than original (like the "usual suspects") but Amazon delivered next day and manufacturer provided a full 3 year warranty ... all the usually sources were 2. "

After being referred to Amazon by laptop supplier, I started buying UPS batteries, power tool batteries, just about all batteries from Amazon ... How is buying many different types of batteries ...specifically stating "UPS batteries" from Amazon , be "totally irrelevant to this topic for many many reasons" .

I was onlineon a Sunday night buying a laptop battery from Amazon as recommended by laptop supplier ... I had previously searched the "usual suspects" sites for a replacement battery and was concerned about the 1 and 2 year warrantees being offered and the fact that most were indicating 1 - 2 weeks delivery. So after completing the purchase of the laptop battery, I went to look at UPS batteries and purchased one with a 4 year warranty and delivered next day. So l fail to see a reason why UPS batteries can not be bought at the same place as laptop batteries.

I'm anxious to hear why:

a) It's OK apparently to buy a laptop battery on Amazon but for reasonsyou didn't explain and that I can't discern, you can't buy UPS batteries there because they are " totally different technology" and a "totally different issue"
b) Where you purchase batteries , .... any battery, ***specifically "laptop" and "UPS" batteries as I stated is "totally irrelevant to this topic for many reasons" ... I am "totally" dying to hear your reasons why.

I specifically recommended buying a UPS battery off Amazon because of my recent experience buying both a laptop battery and a UPS battery there just last month. Let me just add a quote from your subsequent post to put this in perspective.

"The batteries from all the links I provided come with a 1 year warranty. " Potentially getting 4 year UPS Battery warranty would I think be relevant to any battery topic , no ?

1. The UPS battery I bought on Amazon was 9.0 AH instead of the original 7.5 ... Your sites and the ones I looked at offered those also.... Oughta be better 5+ years later.
2. You said all your sources offered a 1 year warranty, the other UPS sources I looked at offered 1 and 2 year warrantees.
3., The UPS battery I bought off Amazon came with a base 2 year warranty.
4. The battery I bought of Amazon came with an additional year of protection "if used in a UPS" .. that's 3 years. (can give ya a screenshot of ya like.)
5. Using an American Express Card on Amazon provides an additional 1 year coverage from AMEX
6. The battery was ordered Sunday night, it was delivered free, the next day, other sites were non-commital on delivery date most saying 1 - 2 weeks
7. I have the same brand battery on my lawn tractor / snow blower... it's 8 years old. They are sold at Sears, batteriesplus and other online outlets
8. Most of the brands and models I saw on the usual UPS battery replacement sites were also offered on Amazon. Many of the batteries sold on Amazon actually come from some of those sites, they are just using Amazon as a storefront.

Seems to me the that battery design totally does not in any way restrict who can sell it nor where one should by it. The only factors affected by where you buy it are warranty, delivery time, customer service and price. Seems to me that the opportunity for longer warrantees, lower prices and overnight delivery is quite relevant to any topic on batteries.... especially when I made a point of saying was buying UPS batteries among other types from Amazon.

My recommendation stands ... consider Amazon as a source for laptop batteries, UPS batteries any batteryas you have a good shot at getting more attractive pricing, quicker delivery times, even better warrantees.

Oh, one more thing worth mentioning ... also ordered a 1500 VA UPS on Amazon ... cheapest price I could find, free delivery, ordered Saturday nite, delivered Monday morning.

 

[Bill_Bright]

Again, laptop batteries have nothing to do with UPS batteries. Amazon sells CR2032 and deep-cycle marine batteries too. Does that make them relevant to this topic? No.

And note I did mention Amazon as a source to check in my post #5 above. But I will point out they do NOT always have the best price as prices change frequently. So again, it is important to check other sources on the day one is ready to purchase. Also Amazon only delivers them faster if the cells you want are in the current inventory of one of their nearby distribution centers.

 

[newtekie1]

Almost true. As I said above, when it comes to the amp-hour specification, you can always go higher (which is why car batteries will work) but you cannot go lower. If your UPS calls for 12V9Ah batteries and you install 12V7Ah, there's a good chance the UPS will simply shut down during a power outage due to the load on the batteries from all the connected devices being too big. Also, the terminal types may matter too.

Yes, but only if you put a very underpowered battery. The reality is you can get away with putting a 7Ah battery in replace of a 9Ah battery. You're run time will just be reduced. I know, I've done it.

But, yes, you don't want to go too small. Otherwise when the UPS starts drawing too many amps from the battery, the voltage will fall too far and the UPS will kick off.

 

[Ferrum Master]

Yes, but only if you put a very underpowered battery. The reality is you can get away with putting a 7Ah battery in replace of a 9Ah battery. You're run time will just be reduced. I know, I've done it.

But, yes, you don't want to go too small. Otherwise when the UPS starts drawing too many amps from the battery, the voltage will fall too far and the UPS will kick off.

The battery internal resistance is higher with smaller batteries as the anode and cathode surface areas differ.

There are protections and under high load the smaller one can trigger soft battery error or simply shut down as the voltage may sag.

It will work for most times, especially with fresh batteries, but when they get a bit older... Disco may come to the town...

 

[Bill_Bright]

The reality is you can get away with putting a 7Ah battery in replace of a 9Ah battery.

Again, it depends on the load.

Just because you can get away with something, doesn't mean it should be done. So I say again, you can go larger with no problems. But you should not go lower.

Why? Because if, for example, you have a 1300VA UPS that uses 12V 9Ah cells and you put 12V 7Ah cells in there, you no longer have a 1300VA UPS. You may have just crippled your UPS and lowered the capacity to 850VA!

Yes, the UPS will work and you will still have the AVR protection which is a very good thing. But if you bought that 1300VA UPS to load up with a power hungry PC (or perhaps two PCs!), a couple large monitors, all your network gear and you are running demanding tasks with that decreased capability, you may have no backup power at all - defeating one of the primary functions of having a good UPS in the first place.

To be sure, IMO it is the AVR function of a good UPS with AVR that is the primary feature of a good UPS. But if I only wanted automatic voltage regulation, I could have bought an automatic voltage regulator (also known as line conditioners) and saved some money. But I wanted backup power too - with enough power to make sure regardless what I am doing when the power goes out, my computer stays running long enough so I can save what I am doing and "gracefully" exit Windows and shutdown my computer.

 

[newtekie1]

The battery internal resistance is higher with smaller batteries as the anode and cathode surface areas differ.

There are protections and under high load the smaller one can trigger soft battery error or simply shut down as the voltage may sag.

It will work for most times, especially with fresh batteries, but when they get a bit older... Disco may come to the town...

Again, it depends on the load.

Just because you can get away with something, doesn't mean it should be done. So I say again, you can go larger with no problems. But you should not go lower.

Why? Because if, for example, you have a 1300VA UPS that uses 12V 9Ah cells and you put 12V 7Ah cells in there, you no longer have a 1300VA UPS. You may have just crippled your UPS and lowered the capacity to 850VA!

Yes, the UPS will work and you will still have the AVR protection which is a very good thing. But if you bought that 1300VA UPS to load up with a power hungry PC (or perhaps two PCs!), a couple large monitors, all your network gear and you are running demanding tasks with that decreased capability, you may have no backup power at all - defeating one of the primary functions of having a good UPS in the first place.

To be sure, IMO it is the AVR function of a good UPS with AVR that is the primary feature of a good UPS. But if I only wanted automatic voltage regulation, I could have bought an automatic voltage regulator (also known as line conditioners) and saved some money. But I wanted backup power too - with enough power to make sure regardless what I am doing when the power goes out, my computer stays running long enough so I can save what I am doing and "gracefully" exit Windows and shutdown my computer.

That isn't how 12v DC batteries work. It certainly isn't going to cause any kind of fireworks or light show having a smaller battery.

The VA rating also isn't going to lower because you put 7Ah batteries in instead of 9Ah. The VA rating is based on the transformer and what it is capable of.

A 7Ah batter can provide the same amperage as a 9Ah battery, just for a shorter amount of time before the battery voltage droops to 10v(the point when the battery is considered dead). This relationship isn't linear. A 7Ah battery, under the full load of a 1300VA UPS, might only last 2 or 3 minutes while the 9Ah battery might last 10+ minutes. In fact, doing the math real quick, if you have a 1200VA load the 7Ah battery will have a run time of about 4 minutes and the 9Ah battery will run for about 6 minutes.(Yeah, most consumer UPSes have really short runtimes under full load.)

 

[Bill_Bright]

A 7Ah batter can provide the same amperage as a 9Ah battery, just for a shorter amount of time before the battery voltage droops

No. Sorry. That is wrong. If what you said was true, the batteries would be rated as something like 12V60m for 12V 60minutes and 12V 45minutes instead of 9Ah and 7Ah.

If what you said was true you could put one of these 12V 9Ah batteries in your car and start the car because you only need a few seconds of 12VDC power. A car battery is just a very big 12V sealed lead-acid battery.

By definition, the 12V9Ah battery is capable of delivering more current than the 12V7Ah battery. The load determines the current needs. A bigger load requires more current.

9Ah means the battery can deliver 12 volts at 9 amps for 1 hour. 7Ah means the battery can deliver 12 volts at only 7amps for 1 hour. Using the basic power formula for DC (Volts x amps = watts) that means the 12V9Ah can deliver 108 watts for 1 hour while the 12V7Ah can only do 84 watts for 1 hour.

A 7Ah battery, under the full load of a 1300VA UPS, might only last 2 or 3 minutes while the 9Ah battery might last 10+ minutes.

No, again, that's wrong. If that 1300VA UPS is running at 50% load, then your scenario is valid. But if the UPS is placed under a full load, the UPS will likely shut down immediately - if the UPS is working properly.

(Yeah, most consumer UPSes have really short runtimes under full load.)

There we agree. But that's okay. The power during a power outtage idea for these UPS is to give the user enough time to finish typing their sentence, save their open documents, exit their open programs, "gracefully" shutdown Windows and power off the computer. And that can easily be done in 4 - 6 minutes - unless it is a really really long sentence!

 

[newtekie1]

No. Sorry. That is wrong. If what you said was true, the batteries would be rated as something like 12V60m for 12V 60minutes and 12V 45minutes instead of 9Ah and 7Ah.

If what you said was true you could put one of these 12V 9Ah batteries in your car and start the car because you only need a few seconds of 12VDC power. A car battery is just a very big 12V sealed lead-acid battery.

By definition, the 12V9Ah battery is capable of delivering more current than the 12V7Ah battery. The load determines the current needs. A bigger load requires more current.

9Ah means the battery can deliver 12 volts at 9 amps for 1 hour. 7Ah means the battery can deliver 12 volts at only 7amps for 1 hour. Using the basic power formula for DC (Volts x amps = watts) that means the 12V9Ah can deliver 108 watts for 1 hour while the 12V7Ah can only do 84 watts for 1 hour.

A car starter draws so much current that even a 9Ah battery voltage would droop to the point it wouldn't work. That goes back to my very very underpowered batter statement.

In a UPS, the current draw difference is small enough that a 7Ah battery will not voltage droop that quickly.

No, again, that's wrong. If that 1300VA UPS is running at 50% load, then your scenario is valid. But if the UPS is placed under a full load, the UPS will likely shut down immediately - if the UPS is working properly.

I literally did the math in the next line. The difference between a 7Ah battery and a 9Ah battery under a 100A load is literally 2 minutes. The 7Ah battery will be able to provide 100A for 4 minutes. There are Ah calculators out there that will tell you this. A fully loaded UPS will not shut down immediately if you use 7Ah batteries instead of 9Ah.

 

[silkstone]

Just to insert an interesting tidbit in here,... that might not help.

The vdroop is caused by internal resistance. And this is what would cause a ups not to work... For reference most lithium cells can deliver 10A before there's any noticeable internal resistance. I'm not actually sure what it would be for the lead acid ones.. The reference to Ah on them is a capacity.

Thered be a difference in max output for each type (large vs. Small) but you'd have to look u the discharge profile for each battery to actually figure out whether it'd matter. For a ups though, they'd need not go above 40A each.

 

[Bill_Bright]

A car starter draws so much current that even a 9Ah battery voltage would droop to the point it wouldn't work. That goes back to my very very underpowered batter statement.

There's a reason AA batteries are used instead of AAA. Yes, time is one variable, but not the only one. And time may not be the deciding factor. Load capacity is another and may be the primary deciding factor.

If you never exceed the capacity of those 12V 7Ah batteries when used in place of 12V 9Ah, fine. But then I would say you may have bought more UPS than you need.

But I say you are cherry picking a specific scenario and using that anecdotal exception to justify your position to use as the general rule.

I am sticking to my position. If you don't want to reduce the load supporting capability of your UPS, and if you want to ensure your UPS properly kicks over to batteries and holds power when on batteries, buy replacement cells of equal or greater amp-hour capacity.

Edit comment: Fixed typo

 

[Ferrum Master]

Yes. Batteries are often used as ideal element at school. But it has parasitic properties, even noise, chemically caused.

It has internal resistance. Due to that there is simple math with inrush current. The steeper the current, the more voltage will sag. Physically smaller battery has higher resistivity(same tech), it's the plate area...

The peak currents can trigger shutdown. Especially when it is colder or the battery is old. Just power up a PC with a crappy 1000KW+ PSU. Some models even pop out 16A fuses while charging the main capacitor. For a UPS it remains the same tough task. There putting a smaller battery can cause troubles.

It is same as with Diesel vs Petrol engine during winter, Diesel needs more current, thus a better accumulator is needed. Plain math really. While new, it can start with any, let it get older or more cold. Petrol doesn't care that much.