Im using some energizer rechargeables, at when fully charged, they top out at 80% capacity (since each cell is 1.2V instead of the regular 1.5V). I used my mouse almost all day yesterday, and it went down to around 73% ... Given that, I expect them to last a month give or take.
not too bad. But, with the original batteries, I got them down to 43% in about a month; so, I'd expect them to last almost 2 months.
So, I think using regular batteries are worth it if you're not a fan of recharging things 😛
I've seen good reviews for the Sanyo Enerloops, but I don't think they will get any better than these Energizers to be honest.