W211 E55 battery/electronics question

[RelentlessForwardProgress]

Hi all, hoping someone has a suggestion.

The battery on my W211 E55 is dead again- no worries, I have a spare. Swapped over - there were some sparks which is unusual- and as soon as I connected the negative the alarm went off with a constant tone, opened the door manually and put key in, dash is dead.

Had to disconnect it as it’s so loud. Has anyone experienced this and has a solution? Has it blown a fuse or fried something? Many thanks.

 

[SL03WLY]

Hi, my battery drain was due to the seat module. But I did encounter an alarm going off when I took out one of the fuses in the panel on the driver side. Could check the fuses in there to see if any are blown.

 

[Wearsthefoxhat]

Fairly big current drain or something left on if larger than expected sparks. Not had a problem with the alarm when replacing either battery on our W211. could be the alarm unit. A day going through the fuses with an ammeter might highlight the current drain.. does everything work or is something a bit “iffy”, suspect.