Over the years I've gone through a lot of batteries for my wireless keyboards and wireless mice. At work, the department bought me a package of name-brand rechargeable batteries and a charger, but I have not been impressed with how well those batteries recharge or how long they last before needing to recharge again.
So when I decided to replace my usual batteries with rechargeables for my home computer keyboard and mouse, I did some research into the best options. All of the most favorable reviews pointed me toward the Panasonic Eneloops (originally a Sanyo product).
While there are different varieties of these (Lite, Pro, etc.), the regular version seemed to suit me fine. I ordered these online on Amazon, and bought enough batteries so that I would always have 4 in the charger ready to use, while the other 4 were in the keyboard and mouse.
These are rated for 2100 recharge cycles, and after 5 years, should still be able to be recharged up to 70% of capacity. Even if I recharged them once a week (and in reality, I don't need to recharge them but perhaps every 2 weeks), they would arguably last 40 years.
I think these have paid for themselves in only a few months, and I am quite happy with the switch from disposables to these Eneloop rechargeables.