Hi there,
I dont think this has been mentioned yet, but some NiMH batteries are better than others. This comes about because of two different specifications, which by the way are not mentioned in any of the ads for the products. We know about the 'cell capacity' rating, which is typically 2000mAh or 2200mAh or similar, but another rating that is not mentioned in any of the ads for standard NiMH cells is the 'capacity retention' rating. This turns out to be a very important rating which needs to be looked at in order to determine absolutely whether or not a given cell will fit your application or not. If this rating is ignored, you may end up with cells that you simply can not use for what you intended to use them for.
Charge retention is the ability (or length of time) of the cell to HOLD a charge once it has been charged completely.
Case in point: Energizer 2500mAh NiMH cells. There have been a million complaints about these cells in that once they are charged completely they quickly loose their charge so even the next day they may not hold more than 50 percent of the original charge. I would not have believed this could happen so fast until i actually had this experience myself and asked Energizer to take them back. Energizer was understanding though and sent me a coupon for 10 dollars USD so i could go buy another product instead. Just to note however they did state that there was no known problem with the 2500mAh cells, so that was typical operation. Was it really just a set of bad cells? I would think so if so many people didnt have the same 'problem'. Was it fixed? I wont buy another set to find out, but instead turn to a new type of cell to recently hit the marketplace...
"Low Self Discharge" NiMH cells (or LSD cells) are cells that hold their charge for several months and loose only a small amount per month. After several months the cells are still very much usable as they still hold much of their charge. These cells are really great. The drawback? The highest capacity at the date of this writing is only around 2000mAh, but that's still very good when you consider that they loose very very little charge in a week.
Case in point: Kodac low self discharge cells. I actually tested four of these cells over a 6 month period and found them to perform exactly as stated by the manufacturer. The charge retention was exceptionally good, meaning that even after a year the cells would still have plenty of charge left in them.
Other manu's:
Sanyo, makes one of the best perhaps, named "Eneloop Cells", comes in colors but the colors may not be available in the US yet (maybe in Europe).
Rayovac, i think they called these "Hybrid Cells".
By the way, these cells come in the package ready to use unlike the standard NiMH.
If you are planning on using NiMH cells for anything you should certainly look into these kind of cells first.