Steve wrote:
a 15 watt solar charger


If you used the battery you're charging to run a clock radio or something,
it might be enough. For a trolling motor battery, a 15 watt charger is a
joke. A typical 10 amp charger uses about 200 watts on the input side to
produce about 150 on the output side.

RichZ©
www.richz.com/fishing