PS I have one car which I use infrequently and unless I disconnect the battery it requires a jump start after about 3 wk or a month. The battery in it is new and the charging system tests fine. I think it is due in my case to standby losses (burglar alarm, ECU volatile memory, etc). Sometimes a defect can occur up which causes a high standby drain - you can have the current measured in your car with ignition off to check that.