I thought rechargeable batteries dissipated their charge over time?

[Sonny]

Here's a shocker...at least to me.

I pulled out some older AA Energizer rechargeable 2300mAh NiMH batteries that have been sitting in my closet for over a year and a half. I put them into my MAHA MH-C801D charger (8 AA/AAA). The charger showed (4) of the AA still had 1/2 a charge left and (2) of the AA still had 3/4 a charge left!

How is this possible?

[shnitz]

The newer NiMH batteries are low discharge. As with every technology, battery makers stopped blindly chasing the consumer-sought rating, mAh, and started focusing on more experience-oriented specs. The same thing happened with computers and the frequency/gigahertz game, and with cameras and megapixels. Anyway, they are supposed to lose only 10% charge over the first six months. As these batteries discharge, the discharge rate goes down. I would guess that it's a half-life style formula, but that's just conjecture. If it's true, then it would be at 90% at 6 months. At 1 year, it would lose 10% again, so it would be at 81%. Another 6 months, and it would be at 10% less, or a total charge remaining of 73%. Nothing works as well as theoretical, plus you may not have the "best" technology batteries out today, so "only" having half charge at the 18-month mark makes sense.

[kenw]

The charger doesn't place much load on the cells when measuring them so they can look more charged than they really are. Placing a more significant load on them and the charge remaining will likely drop much more. If you put them in the camera they will likely drop rapidly to fully discharged after a very short period of actual use under load. However, NiMH do self-discharge more rapidly in heat so keeping them indoors will definitely stretch them. But as mentioned above, newer NiMH cells have even lower self discharge rates that the originals, and nothing like NiCad.

[Shadow]

Get the Sanyo Eneloops. They hold their charge far longer than standard NiMh batteries.