Just registered today. My alarm went off about 1am sunday. Went out to turn it off, car completely dead. Monday we bought a new battery. next weekend same thing happend (car is not used on the weekends). Took the car to advance auto shop to test alternator, they suggested I buy a new one, so I did. This weekend again, my alarm went off and car is completely dead. an uncle of mine said the alarm could have a short. The last thing we hear before the car goes completely dead is the alarm.We've checked and made sure all lights are off and still the battery drains over the weekend. Has anybody had this problem? Any advise would be appreciated.

I'm sure there's a simple explanation for your problem, but we'll need to know what kind of car you have.

2001 C240..

Thanks!

I was hoping you'd say you had an S-Class. It would've been simpler!

I don't know how much experience you have with cars, and there are several ways you can proceed, but here's a few simple things you can check. I'm assuming you don't have the equipment to check the actual "rest current" draw.

First, determine if the alarm is causing the battery to go dead, or, it's being triggered as a result of low voltage. The alarm siren on your car has it's own internal power supply. If it's dis-connected while "armed", it will activate. It's located behind the inner fender liner, to the rear of the right front wheel. Dis-connect it, and look for corrosion at the connector. I've seen lots of them fill up with water.

I've also seen lots of 203's with faulty seat control modules. The seats operate normally, but the modules still cause the battery to go dead overnight. It's easy to reach under the seats to dis-connect them. You can try this and see if the problem goes away.

Ideally, you want to check the actual rest current draw, and diagnose accordingly. I don't know if the guys at Advance Auto will be able to help you. A dealer or qualified indie will be your best bet. Good luck

That is exactly what happened to my 2002 C240. Battery died, alarm went off, replaced battery and it drained. Mercedes replaced a faulty passanger side seat control modules! IT WAS EXPENSIVE!!!!! $700....(also had to replace the driver side seat motor, another 250)
I am trying to get enough info on the web to go back to them and get some money back. I believe I got screwed. Any ideas????