The thing with these wireless mice is that their battery is ridiculously small in relation to their size, they're mostly hollow inside. The battery could double without any consequence (with an insignificant adjustment to weight distribution) or even triple with slight increase to total weight. I believe this to be a type of designed obsolescence since the battery degrades to less than 2 weeks in a matter of ~3 yrs while basically all other aspects of the mice remain nearly brand new. I tried replacing the old battery with an aftermarket Sony battery but it doesn't seem to be completely compatible with the battery management IC of the mouse, so even though it's nominally bigger (1100mah) it only lasts less than 1mo(and the indicator would suddenly jump from full to zero), I've been using my MX Master 2 mostly wired since(and my MX Master 1 initially broke because I cracked a cable dismantling it trying to replace its battery). Even accounting for the degradation of the rubber, these mice should last 5-6yrs, anything less is needless generation of electronic trash.