I have been using a "Battery Tender" for years, small, it works great, doesn't boil the fluid out, keeps it charged. Comes with a quick connector and 2 pigtails, one to hard wire, the other big alligator clips. I hardwired to easy to connect/disconnect without going to battery. When I need to charge something else connect the clips.

$25 at Amazon for 6V

http://www.amazon.com/Battery-Tender-021-0127-Junior-Charger/dp/B000CIPHT4

Mike


1951 Chevy 3600 rust bucket with GarWood dump bed conversion
http://www.flickr.com/photos/mikeybs51chevy