Like many people, I bought some NiMh (Nickel Metal Hydride) rechargeable batteries and a charger but was disappointed with the few weeks of time I would get before they needed recharging. Then I read something interesting about NiMh batteries - they have a rapid self-discharge time. No matter how little you use them, they will be discharged in 90 days.
That sent me looking through the junk drawer for our older-technology, rechargeable alkaline batteries from Pure Energy. We had moved away from them since they don't carry the amount of energy you can pack into an NiMh battery, but a wireless keyboard is perfectly suited to rechargeable alkalines - it draws little current, so a long self-discharge time is more important than stored energy density.
Anyway, the proof is in the pudding, it's been more than 6 months since I had to recharge the keyboard batteries...
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I have similarily bad experiences with NiMH batteries. While on a vacation all my NiMH batteries were only lasting 1 day in my camera and I eventually ran out, even though I brought way more than I thought I needed. I used to get much longer use out of them (used to get 1 pair of batteries to last a week of vacation). I think the problem was my charger, it was a rapid 30 minute charger or something like that. My theory is that each time I had charged these batteries the stored charge got less and less. Perhaps I had a self-discharge problem as well, although I had never had a problem with old NiMH batteries before (or I didn't notice).
I ended up buying a Maha Powerex c9000 charger from here: http://www.paulsfinest.com/Maha-Battery-Chargers-p-1-c-4.html
and I got some of those PowerEx 2700mAh batteries as well.
The Maha charger is great because you can tell it exactly what current to charge with, it stops when it notices the temperature of the battery rising and the voltage tapering off, and you can set it to charge/discharge/charge. Allowing the battery to discharge completely supposedly helps increase total charge with NiMH batteries. The Maha charger can also tell you what the approximate stored charge is (if you ran a program that contained a discharge cycle). Anyway, my point is that a lower total charge could also reduce the self-dischange time even further, and a lower total charge could be due to a crappy charger. I've had good luck with the charger so far.
I noticed at http://www.paulsfinest.com/Maha-PowerEX-Batteries-p-1-c-5.html that they are selling some "low-discharge" NiMH batteries now called Imedion (but with less total charge of 2100 mAh instead of 2700 mAh). Never tried them.
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