I have been using one from Harbor Freight that cost less than 10 bucks.
http://www.harborfreight.com/automot...ger-69955.html
it a will keep the batteries topped up with out boil over. does not use a lot of electricity during the month.
while not as fancy as the ones mentioned above but a good way to keep batteries charged, they will not really charge the battery for the most part, just keep them charged up.
I put one on my truck which has two batteries, diesel truck, with voltage at 12.6 which is a bit low. After a month the voltage, after sitting a bit, with no load was up to 12.75 which is considered full storage for a 3 yr old battery.
I take the batteries out of the AS during winter storage, put in garage on floor, hook them together with some solid 12 ga. wire and hook the little maintainer up and let them sit.
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Carl, Raleigh NC
2-24-16 got a 2005 Classic 31D
460 watts solar, lithium 230 AH, 16" LT's, pulled by:
2003 F-250 SD, CC, 7.3L PowerStroke
WBCCI#1691,
Piedmont Airstream Club, Unit #161, Region #3