[chainring]

Very good summary, and only some additional points.

Originally Posted by jj2me

Just to sort of summarize: There are basically three types of rechargeable AAs available today (ignoring the older NiCad because of its lack of any real advantage):

NiCd, while being difficult to find these days, still do offer an advantage. They're robust and incredibly tolerant of abuse. Even with that advantage, there's too many downsides to consider them: price, lower capacity, bad for the environment.

• low self-discharge NiMH, like Eneloops, Rayovac Hybrids, Rayovac 4.0, etc. Advantage: slow discharge when not in use.
• regular discharge NiMH, losing 1% charge per day. Advantage: comes in higher mAh ratings.
• rechargeable alkaline. Advantage: 1.5V instead of 1.2V.

• Slow discharge translates into less maintenance to keep them vibrant.
• Watch out for cells over the 2000 - 2100mAh rating. There's tons on the market claiming high capacity, but the reality is lots of them are overrated quite a bit. Maha PowerEx 2700 mAh AA's are very good in testing close to their rating.
• Rechargable alkaline: rechargeable or non, if your device wasn't made for NiMh or NiCd, you're generally stuck with alkaline or primary lithium. You *may* get away with a really good performing NiMh, but the device will probably go to a low battery condition before depleting the battery's full charge.

Rule of thumb:
- Use Eneloops et al. if you often don't use your reader for days.
- Use higher mAh rated regular NiMHs in a device requiring more juice, like a digital camera. Also use them in a reader that you use daily, though I don't know at what level of use the plot of the higher mAh/higher self discharge battery crosses that of the lower mAh/lower self discharge battery.
- Use rechargeable alkaline only if your device requires 1.5V, and won't work on anything lower, and you prefer rechargeables. Rechargeable alkalines are also slow self discharge, which made them attractive before low self-discharge NiMHs were invented. But rechargeable alkalines have several disadvantages: not popular and not sold many places anymore, require special charger, offer many less recharge cycles before they're bad (maybe as few as 12), lifetime number of cycles is lessened substantially by deep discharges, offer less mAh with each charge cycle. I suspect most people would rather just use regular non-rechargeable alkalines.

- Nothing to add since the Eneloop has been covered enough already.
- Just a point of clarity between Eneloop/LSD (low self-discharge) and higher capacity non-lsd NiMh. It's not so much that the traditional cell is better suited to devices that require more juice (read: high drain), because the LSD cells, especially Eneloop, can sustain high amperage draws (up to 10A). It's that the higher capacity non-lsd cells are just that, higher capacity. With something like the Maha 2700's, that will translate into more runtime than the Eneloop, all else being equal, and both being hot off the charger.
- Alkaline batteries, either primary or rechargeable, have one huge and serious disadvantage for me. They LEAK! I've had new ones leak, not so new that leaked, and old ones that leaked (understandable). Regardless of the age, leaking alkaline and the possibility of it happening just isn't worth it to me. I have some Stabila electronic levels (expensive level with a digital module) that came with some high end Duracell alkaline. Upon receiving the levels, I replaced the alkaline with Eneloop's.