NiMh batteries need to be Form Charged the first few times they are charged, this is accomplished by charging at C/10 for 16-24 hours or till the battery starts to get warm. if you do not form charge them they'll false peak when used with a peak detector and never achieve their designated capacity.

over time and many cycles they can be form charged to help bring them back up to par when they seam to just not put out what they once did, often it'll bring them back to full capacity and you can go back to quick charging/peak detecting.

kc