Best answer, don't buy logi any more. I have MX2 and MX3, I suspect the battery is fine in the MX3 as it works for literal weeks on the red light flashing randomly for days at a time, charge it, no difference. Checking reddit, the popular theory is warranty burnout, so the solution is to stop buying these expensive devices that are on the whole no better than something half the price if you look around, and last exactly until warranty expires before starting to randomly play up, strangely enough.