The batteries themselves are not the thing that varies in price so much, it is the charger. Some of the best around are Maha and the main place online to get them is
Thomas Distributing. The most important thing IMO is to get a charger that has an individual charging circuit for each cell. This prevents any from getting over charged or under charged. Under charging just leads to less juice, but over charging can ruin the cell.
I personally went with a Duracell charger from
Walmart that came with four cells for $18. It has the individual charging circuits. So far so good after about five months. I use Energizer 2500 mAh cells. The higher this number, the more it holds. One last thing to look at. If you can see in the packaging well enough, try to get ones that were made in Japan instead of China. I have no proff that they are better, but I have heard this many times.
Kevin