I did same thing here but used one of those small 10WATT solar panels sitting in my windshield area. Put a 12V plug on it and plugged into an always live 12V socket in the truck. Does a great job keeping my truck start battery a trickle charge.
The solar panel is cheap around $20 from local auto parts store...
This way I didn't have to worry about finding 120VAC somewhere to plug into it. Always sunlight during the day... Even cloudy days it is usually still putting in a small charge...
I got this idea from my battery bank replacement ongoing project. I'm going to use a TORKLIFT slide on lid battery box and it came with a one solar panel for the lid. Since my battery bank has two groups of GC2 6V batteries I am going to order a second solar panel and then each group 6V batteries in series will always be getting a 12V small trickle charge... The slide on panel already had the mounting holes punched in on both sides...

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Roy Ken
