Dell Latitude 5420 i7-1185G7 throttles to 400MHz on battery power

[disarray]

Hello TS community

My work laptop has been unusably slow when unplugged - even the mouse is lagging - meaning no way to work away from a power source regardless of charge. I've read and tried forum posts here, including one about another Latitude machine, and other resources online - but reset back to default settings now, hope to find help here to diagnose the issue and at least regain the ability to browse webpages and use outlook word excel etc. on battery power.

Please let me know what other logs or information I could provide, and thanks very much in advance.

Dell Latitude 5420 i7-1185G7 32GB RAM
Windows 11 Build 22621
65W Power adapter
1 to 2 external monitors (HDMI + USB-C)
No undervolting (though before I updated to Win 11 I had used Intel XTU to undervolt, seems it has been reset by now)

Things I tried, and have since reset, with no improvement. Though sometimes the max speed can be maintained or down to around 1GHz for a few minutes after unplugging but eventually goes down to 400MHz
- intelppm start value set from 3 to 4 in Registry Editor
- unchecked BD PROCHOT
- Power Limit 4 Max set 0 in TPL
- checked MMIO Lock in TPL
- checked Speed Shift EPP at 128, 96, 225
- Speed Shift in TPL: Min 4/24 Max 42/48
- PL1 PL2 set 60/100 in TPL

Once I plug in the power adapter, speed returns to normal.

Screenshots on 65W Adapter (220V): All 3 EDP Other flashes red every few seconds, PROCHOT 98C sometimes red

On battery power: PL2 solid red for Core and GPU, flashes red for Ring

 

[PHVM_BR]

Check the battery life with HWiNFO64.
It may be that the battery is at the end of its life and the CPU is severely limited when unplugged.

Try unchecking BD PROCHOT in the Throttlestop main window.

No undervolting (though before I updated to Win 11 I had used Intel XTU to undervolt, seems it has been reset by now)

i7-1185G7 cannot be undervoltaged.