12V fans query

As an experiment with no load other than DVM , neg to neg, 12V dc , 0.2A fan , 1 foot from the nozzle of a 1KW fan then 17volt output from the fan I tried.. Must have contained segmented magnets. Turnuing the fan the other way in the airstream still produced "positive" voltage. I didn't try it any closer.

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

That rather depends on the construction of the plates in the battery, which determine whether or not it is a genuine deep cycle battery, which is good to 20%, or a sponge plated hybrid which is labelled "deep cycle", but is only good, as you say, to 50% if you want a long life. Genuine marine quality deep cycle batteries, as Michael suggested he was using, should be of the former variety. The latter tend to be general leisure batteries, as far as I know.

Arfa