XM Radio and car batteries

I have a 2002 Mercedes C 240. When I bought the car it had XM radio already installed. Shortly after, I started experiencing dead batteries.

I took it to a repair man and he said it was the seat sensor and “fixed it” for $500.00.

The problem remained.

A few other mechanics AND myself suspect that it is how the XM radio is wired.

Has anyone else had any issues with their XM radio and car battery?

Another dead battery! We get this question a lot… and none of the previous posters ever mentioned XM radio.

There are many possibilites. There is the status of the charging system, the condition of the battery itself, and there can be corrosion in the battery connections. Any of these conditions can be the root of your problem and must be checked out first.

If the battery and alternator are OK then you have some accessory that is always on and is draining the battery. Folks have found trunk lights or glove box lights that are on at all times. These situations are detected in the usual fashion, by taking an ammeter to the electrical system. The process is simple enough but it can be time-consuming.

It is clear that your mechanics (and you) are simply making wild-eyed guesses. Maybe XM radio is to blame, most likely it’s completely innocent. Take your car to a real mechanic who will reach for his ammeter and track down the problem the right way.

Normally this kind of trouble is located by measuring the battery current drain then by pulling fuses the circuit is pinned down that has the excessive current flow on it.

You spent a lot of money to have this fixed and perhaps the seat sensor was a problem but you still have the same trouble. I would take the car back to the shop and have them see what is going on. You paid them to do that already.

The radio may be the trouble but I doubt it is. It should only need a small amount of current for the memory.

A few other mechanics AND myself suspect that it is how the XM radio is wired.

I have never heard of such a thing. Why would you or the mechanics suspect the radio. It is possible, but it is way way down my list.

I have to go with Mr. Meehan here. What makes you suspect the XM? Is it a factory installed radio?

After checking the battery and charging system, put a current meter on the battery and start pulling fuses until the load goes away. Then figure it out from there.

I agree with the others, the radio seems unlikely. Have you had the battery and the charging system checked out? How quickly does the battery go dead if the car is unused? If there is actually a current draw on the battery, it will have to be narrowed down at the fuse box, tedious but not difficult. If you really suspect the radio, try removing (unplugging) it and see if the problem goes away.

It might be the radio, but I doubt it is just because it is XM. When the car is turned off, the radio shuts down, including the XM receiver.

Have same problem with both my cars,
2009 Volvo C30 & 2017 Forester XT.
Was told by mechanic @ Volvo that this was the problem.

You took your Forester to a Volvo dealership?

Yes, I thought that was… odd.
In any event, my 2011 Outback, equipped with XM radio, has never experienced any battery problems.