Whats wrong with my car...?

[TTmonkey]

The car lives in the garage, its only used in nice weather (so not as often as I'd like).

If I leave it for a week, the battery doesnt have enough charge left to turn the engine over....

Its had a new battery.

It doesnt have anything turned on (I've checked), and I dont even lock it.

What is causing the battery to discharge?

Cheers

[Howard-]

Connect up a multimeter to the battery to measure the current draw, then start pulling fuses to find out.

[EddieFelson]

Get an electrical tester and check the draw on the battery. Then if there is something thats slowly zapping the battery go through the fuse box one by one checking the draw on each, you'll find the circuit that's draining the battery.

Also check the alternator is charging the battery.