I did this fix on two mice, and a search shows there is others having the same issues with it. Also see the location of the removed resistor, it is close to the crystal. The solution is to disable the LEDs by removing R8. The main blue sensor illuminating LED is also driven from the same source, but this makes sense due to the higher Vf of the blue LED. It turns out the LEDs where driven from 4.5V from a DC/DC converter and wasting a lot of power through the limiting resistors. I never saw the warning light, because the increased current immediately drags the voltage below to cut-off limit and it turns off. Moving: 15mA Idle: 0.7mA Low battery warning, red LED: 90mA. I measured the current drawn from the single AA battery: First 14 seconds after turning on, green LED lit: 140mA (!!) This causes the battery voltage to sag below the cut-of voltage unless the battery was fresh, and turn off the mouse.
It had a battery life far away from the claimed 8 months. If I left it on, it worked a few weeks longer, and when it turned itself off again the battery had about 1.1V. If I tried several times it finally stayed on. My mouse was difficult to turn on even if the battery had 1.4V left on it.
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