Draining battery

[lambert.john]

My battery has been draining power whilst I sleep - literally.The problem has appeared only recently but if I leave the car unused for two (or more) nights I find the battery flat and won't turn the starter motor. I replaced the battery with a new one but with the same result. I have overcome the problem (for now) by disconnecting the battery overnight, which solves the issue, albeit with the hassle of having to reset the clock each time!

What could be causing this? I do have an aftermarket alarm system (which I don't use when the car is garaged). This has not caused problems up till now but I'm wondering if this could be the culprit.

[Alan_M]

Alarm is a likely candidate, as is the radio or boot light.

Easy test for boot light - stick phone in there and record if light goes off.
Radio - pull fuse or disconnect.
After that you will need to get your multimeter out and test each circuit for parasitic drain.

[rbgosling]

You can get a handy device like this:



that looks like a fuse and you can connect to your multimeter. That way you can pull each fuse in turn and see which circuit has any current in it.

[Marten]

You can get a handy device like this:



that looks like a fuse and you can connect to your multimeter. That way you can pull each fuse in turn and see which circuit has any current in it.

Or connect an ammeter between earth lead and battery. (range on 10A or a spike when connnecting could blow a fuse in the meter). Then you know the current draw and you can start pulling fuses to see which circuit gets you closer to the problem. With doors closed the draw should be minimal in the miliamps range