Using a Trickle Charger

New user here with a question on hooking up a trickle charger to a 2003 SL500.  Since the car sits for a few weeks at a time, especially in the winter, I have plugged a trickle charger into the cigarette lighter. 

Using the Mercedes Dealer's charger and now with an aftermarket one, the SOS light in the overhead console lights up when plugged in.   Has anyone else experienced this?  I have received varying answers from the dealers about it and finally the technician at SOS says that the Mercedes charger, and probably the aftermarket one, are not meant for the Glass Matt (sp?) batteries that are in these models.

Does anyone else use a trickle charger during non-use time?

If it's really a trickle charger I wouldn't use it. You don't want to use a trickle charger for a long period of time. Maybe a day or two, max. There are some very good battery managers available for about $20-$30.

I have one I bought from Sears on my John Deere. It's a 12-volt manager. A unit the size of two decks of playing cards. It's connected to the battery and has an AC plug. I had one on my '00 Corvette for about six months.

A better one, the Battery Tender, is on my '01 Corvette and has been since I bought it. This has just a couple of wires connected to the car battery and a separate unit about fist-size that accepts those wires and has an AC plug. I got mine at PepBoys.

I don't know about a Glass Matt battery. It wouldn't surprise me that MB would do something stupid, though.