RaceItAgain, I would be happy to provide schematics, parts lists, etc. I have been trying to do so for general viewing on this site, but for some reason the photo gallery refuses to let me log in. I am trying to get that fixed through the normal channels, but in the mean time, if you want to PM me with your E-mail address I will send you the info that way.
BOb86ZZ4, The cheap LCD readout in the cigarette lighter is a fine idea. I don't know how accurate it is, but it is probably accurate enough. 11V is a little low. It depends on the exact battery type, but in general 11V is probably about 90% discharged. I know they are called "deep cycle" batteries, but for maximum life you should never go below about 40% of full charge.
The 9V regulator is needed because the so called 12V batteries can easily reach 14V when charging, and that is more than the specifications for the LED readout allow. The LED readout might tolerate it anyway, but as a conservitave design engineer I don't like to push specifications.
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