The battery in my 1996 850 wagon has gone dead while the car sat for a week on two occasions - once 6 months ago, and once recently. Each time, I jump-started the car and it has started and run without a problem afterwards, as long as I use it on a regular basis.

Does anyone have any advice about whether this is a short or a battery that won't hold a charge? The battery is a two-year-old Interstate, so it *should* be OK... The charging system seems fine, giving 13.6 V when the engine is on. I checked for stray lamps that might be on, and didn't find any.. (might there be a tricky one?). One last test I did was to check the quiescent draw on the battery with everything off - removed the positive terminal and attached an ammeter between the battery post and the terminal. I measured about 150 milliamps. I know there is always some draw because of anti-theft, keyless entry, and various other systems, but I have no idea whether this is too much or about right. Can anyone give me a ballpark?

Any advice or experience with this problem would be greatly appreciated!