If you use Optima gel cell batteries, I'd recommend getting one of their units. They will sometimes become unchargable by regular chargers but the Optima chargers can often bring them back. A friend with a large collection picked one up and brought a couple of long dormant gel batteries up to snuff. Not cheap but batteries aren't too cheap anymore either.
http://www.optimabatteries.com/en-us...FQlafgodZHYAEg