If you have access to 110v you might want to pick up an inexpensive battery maintainer. You can get one at Harbor Freight for less that $10, I believe it puts out 500ma? That may not be correct, but it isn't much, disclamer says they will not recharge a dead a battery. It just puts a contiuous small amperage charge at 13.5 volts into the battery. They are different than even a trickle/float charger. I keep the boat batteries on one each over the winter. It should be enough to keep the battery up?