Help! Slow Battery Discharge

BILLGRISSOM is correct.

A newer Gm product with RVC charging systems that started on the trucks about 05 although the updated version in 08 is worse and GM cars, some starting in about 04 like the Cobalt will kill a battery in 30 days if not started. It is due to the BCM controlled charging system and the draw only occurs 1-2 twice a day for short periods of time hence the 30 days. The BCM wants to know Battery state of charge and generates a temp current draw, enough to kill a battery in 30 days.

A Chrylser product like a Caliber can kill the battery in 20 days if not started during the time frame.

Also the latest cars are now using a new second "B" BUSS or MID -SPEED BUSS, that controls the power draw of multiple computers. These may take up to 30 mins to stop drawing current after the key is turned off some if you are perfroming a draw test. The BUSS has to go to "sleep" first before you can get a real current draw value.