I changed to NiMH batteries a few years ago, and went for high-capacity 1400 mAh packs.  From the start, the packs never achieved their rated capacity.  Other skippers I spoke to said either the same thing, or that their packs achieved their capacity but never exceeded it.  By comparison, NiCd packs routinely exceed their nominal capacity.  I have heard that the system for designating NiMH capacity is technically different from the system for NiCd, such that NiMH cells are more over-rated than NiCds, or, the same thing, NiCds are more under-rated.

Over the last two years, my NiMH packs have gradually lost their capacity.  They now can only manage about half of the capacity they originally had, having been simply recharged from whatever state they were in about 20 times, and cycled (discharged, charged, discharged, charged) about 20 times.  Again, other skippers I have spoken to have said the same thing -- their NiMH packs have gradually lost significant capacity.  By comparison, NiCd packs easily retain capacity over 100 charge/discharge cycles.

So I've gone back to 1100 mAh NiCds.  Cheaper, and in fact their capacity is as good as the NiMHs were.  I use the (UK-based) Mainlink Electronics' "Digilyser" unit and now routinely run two discharge/charge cycles every week, so should not be troubled by any "memory effects".

Update

I've had some comment from other skippers.  Some reckon they don't know what I'm talking about, and are very satisfied with the NiMHs.  Exploring further, it seems that they don't cycle their NiMH battery packs.  They just re-charge 'em whenever they want.  Maybe NiMHs don't like being cycled.

2005-12-18

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