You don't really want to put a trickle charger on any car that is left unattended, can cause damage. There is a product out there called Battery Tender that is made just for these situations. It charges the battery and shuts off when fully charged as the battery starts to discharge it senses it and starts to recharge automatically. My brother-in-law has a 2nd home down here in Fl and his ES300 constantly had to be started every few weeks or jump started until we bought the Battery Tender. He now uses it on his Highlander and has never had a problem even after not starting for 4 or more months. My next door neighbor tried the trickle charger bit on his Mercedes and wound up with a ruined battery and damage to the electric system.

http://www.batterytender.com/