Software

As expected, the M65 RGB Ultra Wireless is fully compatible with iCUE, Corsair's capable yet incredibly resource-hungry software. For whatever reason, the nonsensical distinction between hardware and software mode for CPI adjustment is still present. Furthermore, the lighting brightness slider continues to be hidden under device settings instead of lighting settings, where it would make sense to have it. Apparently, Corsair is well aware that the way these options are laid out isn't the most intuitive, and thus implemented several tool tips to further convey to users how things work. Of course, the more elegant solution would have been to make the UI itself easier to grasp in the first place. Another curiosity is the fact that the hardware profile may only be modified if the mouse is plugged in.

All options are available through multiple list entries. All buttons except the left main button can be remapped to mouse, keyboard, media, or macro functions. CPI can be set for up to five color-coded stages, ranging from 100 to 26,000 CPI in increments of 1 CPI. "Gestures" allows one to setup functions that are executed upon tilting the mouse in a specific way along the four possible axes. The threshold angle can be specified in degrees, and one can set it up in such a way that it isn't necessary to return to neutral position in between gestures. Additionally, a surface calibration can be performed to lower the lift-off distance beyond the default level. Further LOD adjustment options are present under device settings, allowing one to choose between five presets (lowest, ultra-low, low, medium, and high). Polling rate adjustment (125/250/500/1000/2000 Hz) too is found under device settings, and the device is still restarted every time the polling rate is changed, which can get annoying rather quickly. Unlike on the Sabre RGB Pro Wireless, the polling rate doesn't have to be adjusted under device settings of the dongle. Under device settings, one also finds a setting called "Button Response Optimization." With it set to on (default), proper debouncing is performed, increasing click latency but reducing the likelihood of so-called slam clicking. By setting it to off, debouncing is no longer performed, which lowers the click latency, but introduces slam clicking. Furthermore, angle snapping can be turned on or off.

On my system, the software has a RAM footprint of 421 MB on average when running in the foreground, along with a considerable CPU and GPU time cost, which go down slightly when minimized to the system tray. Upon exiting the application, several processes keep running, totaling a RAM footprint of 41 MB on average and taking up CPU time even though iCUE isn't running. In fact, even when setting iCUE not to launch on startup and not launching iCUE, several processes will load nonetheless on startup, even including the infamous Corsair headset drivers, despite me still not owning a Corsair headset. Lastly, iCUE installs no less than four driver packages, including for non-present devices, not all of which are removed upon uninstalling. Hence, one has to run pnputil /enum-drivers and remove any leftovers manually.

Lighting

The M65 RGB Ultra Wireless has but a single lighting zone, which is the logo at the back. Without iCUE running, four different lighting effects can be set up and saved to the on-board memory: Rainbow, Color Pulse, Color Shift, and Static. While running iCUE, a whole slew of lighting effects is available, including shift, blink, gradient, and pulse effects, many of which can be further adjusted in terms of transition speed, direction, and color palette, not to mention the ability to synchronize them with other Corsair devices. Of course, the lighting also can be disabled altogether.

Color accuracy and vibrancy are excellent throughout. Here's a short demonstration video in which I go through the Rainbow, Color Pulse, and Watermark Spectrum lighting effects:

Battery Life

Without illumination, Corsair states a maximum battery life of up to 120 hours using Bluetooth and up to 90 hours using 2.4 GHz. No details are provided in regard to polling rate for the latter, so I'll assume it refers to the default 1000 Hz setting. Corsair iCUE includes a basic battery life indicator, but instead of being percentage-based, it merely discriminates between descriptions (I only ever got to "high"), which are essentially useless. As such, I'm unable to gauge anything.

Within iCUE, one can enable sleep mode and define after which period of inactivity sleep mode is entered. By default, this is set to 15 minutes, which is way too high and thus should be lowered to a more reasonable figure such as two minutes. Furthermore, one can enable Power Saving mode, which merely disables illumination.

Using the included USB Type-A to Type-C charging cable, I measured the charging speed during the constant current stage, which sits at around 0.360 A. Unfortunately, I'm unable to determine the battery capacity, though its size makes me believe it is in the range of 1000 mAh.