Energizer Rechargeable Batteries, AAA, 4-Count, (Pack of 2) Review

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(More customer reviews)All rechargeable battery manufacturers love to boast about their product's current capacity (mAh). But there is a dirty little secret that they don't want you to hear: self-discharge rate. Simply put: a fully charged NiCd or NiMH cell will gradually lose its stored energy over time. Technical papers I have researched typically put the self-discharge rate at 10-20% per month for NiCd cells, and 20-30% per month for NiMH cells. This kind of self-discharge rate is usually acceptable in applications such as digital cameras.
I bought 8 of those Energizer 2500mAh rechargeable NiMH batteries over one year ago. At first, I was very happy about the large current capacity offered by those batteries. But within a few months, I started to notice that they die very quickly in my digital camera. In fact, a set of Sony 2300mAh NiMH batteries I bought one year earlier seems to last much longer when used in the same camera.
I recently did some controlled experiments (using the LaCrosse BC-900 AlphaPower Battery Charger) and found out what's wrong: The Energizer NiMH batteries have very high self-discharge rate. After fully charging all 8 cells and left them on the shelf for one week, five of them lost over 30% of their charge, and the other three lost about 20%. In comparison, the set of older Sony batteries only lost around 10% over the same one-week period.
So what this really means is: if I charge up those Energizer 2500mAh batteries and leave them in my camera for three weeks, they will become totally exhausted. I found this kind of self-discharge rate completely unacceptable, therefore I strongly advise against buying those batteries.
[Update on April 9, 2007]
I have hardly used those Energizer 2500mAh cells in the last few month. Now they have deteriorated even further. Five of them can't even hold their charges for more then a day.
Instead of the Energizer 2500mAh cells, I recommend buying the Rayovac "Hybrid" 2100mAh cells. They have very low self-discharge rate (see my review on "RAYO 4PK AA") and are cheaper than the better-known Sanyo eneloop 2000mAh cells. Kodak also sells a "Pre-Charged" NiMH cell with exactly the same spec as the Rayovac Hybrid.
The bottom line: Low-Self-Discharge NiMH cells are your best choices. There is absolutely no point in taking chances with older generation 2500-2700mAh NiMH cells now.
[Update on Oct 20, 2010]
The product image of Energizer Rechargeable AA has changed. It no longer advertises '2500mAh'. I went to my local W*mart to check out the actual batteries. All Energizer rechargable AA cells are now 2300mAh. Evidentially, Energizer has 'rollled back' battery technology to 2004. This is actually a good move because the lower capacity cells do not suffer from hideous self-discharge rate. Contrary to popular belief, a 2300mAh cell is not any less capable in delivering high power than a 2500mAh cell. Just that the run time will be about 8% shorter.

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Energizer Rechargeable batteries are great for use in your household devices, such as digital cameras, toys, remote controls, flashlights, and portable audio players. The Energizer Rechargeable AA battery continues to last 4x longer in digital cameras, hold its charge up to six full months, and now can be charged up to 150 more times.

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