Consumer Battery Replacement
 

I noticed that over the past year, the Convenience Functions Offline message has been appearing more and more frequently. When I purchased my SL two years ago, this message appeared after about a week but now, it shows up after two days. I have read previous post about this and realize that I might have to replace the rear battery. I haven't checked with the MB dealer about the cost of a replacement but wanted to know if anyone here replaced it with an Optima battery (either red or yellow top), or something else that is equivalent to the OEM.

I had to replace mine last month, expect the battery to cost ~200. I put it in myself so the install cost was zero. The owners manual has the procedure for replacing the battery.

I was unable to locate a non-mb replacement through the usual channels. I think this has to do with the way it bolts into the trunk.

Here is another thought: Something a lot of people are not aware of is that car charging systems are notorious for insufficient charging of really depleted batteries. Your car is a 2006, the battery might still recover with a full external charge. Naturally, car dealers want to sell new batteries and will not make an attempt to really check the battery condition - maybe you have a buddy with the equipment to do that. And if you don't drive the car frequently, a trickle charger - or a one weekly full charge with an external charger - is a must or the battery life is severely reduced.

I realize that if your battery is beyond a certain low re-charge cycle threshold, you have no other choice, but I know from experience that many good car batteries are discarded just for the sake of a small profit for the dealer, a total waste!

replace the battery and get a trickle charger installed if you don't use the car as a daily driver otherwise, that battery doesn't last very long. Not sure about non MB battery for that slot, it's a small battery and not sure if anybody makes a battery in that size. :word:

Thanks for the replies!
 

That is a good idea CA E55, I will remove the battery from the trunk and charge it. If it cannot hold the charge, then I'll buy a replacement along with a trickle charger. The battery looked like a standard size the last time I looked at it but never looked at the tray or tie-down mechanism to see if those are compatible with a standard-size battery.

Are there any special precautions in removing the rear battery? Is there anything I need to "reset" when I reinstall the battery?

Get a battery maintainer
 

Wouldn't it be easier to get battery maintainer (not trickle charger) like Battery Tender plus or Battery Tender Jr before taking the battery out? Amazon have it for $25-$45. Connect it to your rear battery to charge/condition your battery. Battery tender comes with wire looms that can be connected to your battery hence making it easier to connect the charger when the car is not used/driven.

Most of the time, the battery just need a good slow charging/conditioning (with Battery Tender) instead of the fast charging by the car alternator or regular battery charger.

Make sure you get Battery maintainer not trickle charger. Trickle charger is a constant charger while battery maintainer will adjust charging based on the state of your car battery.