Looks like you have an 04 so check out pages 298 and 299 of your owners manual. Looks sort of straight forward. But if you are having an 04 battery go "flat" in a week of non driving you are experiencing battery drain somewhere. Might be smart to take it into a dealer next time you get it cranked up. They should be able to check out battery drain as the 12 V system should be similiar to a standard Toyota.