My battery only dies when the car is parked

Hi @michaelpbrodie,

Check that the courtesy light in the boot (trunk) has been switched off. If left on permanently it can drain a battery overnight and it won't be noticed that it is on, unless the boot is opened and even then not if it is thought to be set to turn on/off when the boot is opened/closed.

If you have a DMM (digital multimeter), use it to measure what the quiescent current draw is when the car is parked and nothing is turned on i.e. key out of ignition.

Set up the DMM to measure DC Amps 10A scale.

Disconnect the -ve battery cable from the car battery and connect the DMM between the -ve battery cable connector and the -ve battery terminal and check what the reading on the meter is.

With most vehicles the current draw with nothing turned on is between 50-80mA i.e. 0.05A-0.08A .

If the meter shows a lot more than this amount, start removing the fuses in both fuse boxes i.e. passenger compartment and engine bay, one by one and checking the meter when a fuse is removed (replace the one removed before removing the next one) until the correct current measurement is displayed. It's quicker if there are two people doing this especially when removing the fuses in the passenger compartment.

Once you know the fuse that when removed restores the current draw to a more normal value, check what its function is by looking at the fuse layout description either in the lid of the fuse box, in the owner manual or online.