Ordinary 'high-capacity' NiMH cells typically advertise charge capacity of 2500-2700mAh (for AA), but they all suffer from rapid self discharge problems. That is why I switched over to low-self-discharge (also called 'Pre-Charged') rechargeable batteries more than four years ago, starting from the original SANYO eneloop
. Over the years I have tested many other name-brand LSD cells such as Rayovac Hybrid
and Kodak Pre-Charged
, all with great results.
The only drawback of LSD cells is lower capacity. First-generation LSD cells are typically rated at 2000-2100mAh. Recently, I have seen arrival of second-generation LSD cells with higher capacity, such as these IMEDION AA 2400 mAh low self-discharge batteries
. Here are my test results, using the La Crosse BC-900 battery Charger/Analyzer
- Right out the package, the average remaining charge is 1880mAh for a set of four Imedion AA cells. This is about 78% of the rated capacity, which suggests those are indeed low-self-discharge type (ordinary NiMH cells typically arrive exhausted)
- After just one Charge/Discharge cycle, the average capacity improved to 2455mAh, or 2% higher than rated capacity. This number remains the same in subsequence cycles. Again, this performance suggests that those cells are LSD type (ordinary NiMH cells typically takes ~5 cycles to slowly approach their rated capacities)
Just for comparison, here are my test results for other brands of LSD cells:
- Sanyo Eneloop XX
: Rated 2500mAh, measured ~2600mAh (4% higher)
- Yuasa Enitime PLUS
: Rated 2500mAh, measured ~2400mAh (4% LOWER)
- Lenmar R2G AA
: Rated 2150mAh, tested ~2030mAh (6% LOWER)
- GP Recyko NiMH AA
: Rated 2100mAh, tested ~2230mAh (6% higher)
- UltraLast Green Everyday Precharged
: Rated 2100mAh, measured ~2200mAh (5% higher)
- SANYO eneloop (2nd-gen): Rated 2000mAh, measured ~2130mAh (6% higher)
The measured capacity of IMEDION AA cells (2455mAh) is higher than all others except for Sanyo XX (2600mAh). However, as of this writing, the Sanyo XX costs nearly twice as much as the Imedion. That makes those Imedion LSD cells a much better deal compared to Sanyo XX. When comparing Imedion to Sanyo eneloop, you pay ~15% more for ~15% increase in capacity. So again, this makes the Imedion a great deal.
One important side note: The Imedion AA cell is quite a bit thicker than normal alkaline cells. So they may not fit in appliances with tight battery compartments. This is actually a common problem with high-capacity NiMH cells. I don't have a pair of calipers to measure the cell diameters. But in term of relative 'fatness' of various AA cells, I can arrange them in the following order:
IMEDION > Sanyo XX > Sanyo eneloop > Rayovac Hybrid > Alkaline
[Update on Oct 23, 2011]
Tested a pair of Imedion AA after 5 months in storage. The average remaining charge is 2125mAh, or 86% of the original capacity (2470mAh). This charge retention rate is almost as good as that of Sanyo eneloop.
[Update on Mar 31, 2013]
Tested a second pair of Imedion AA after 17 months in storage. They retained 75% of original charge. This means the Imedion's self-discharge rate is just slightly faster than that of eneloop. For all practical purposes both are excellent.