Hi everyone, I feel a bit stupid asking this but I've owned my Mercedes S Class for about two years now and I still don't fully understand how the dual battery system works. Last week I got a message on the screen saying auxiliary battery malfunction and at the same time the eco start stop feature stopped working. I took the car to a local garage and the guy told me I need to replace the small auxiliary battery under the glove box which he quoted 550 dirhams for. But then he also said I should consider replacing the main starter battery at the same time because it's three years old and might fail soon anyway. That would cost another 950 dirhams plus installation. I'm not sure if he's being honest or just trying to upsell me on stuff I don't actually need. I started reading owner forums and some people say you should only replace the battery that has failed and others say you should always replace both at the same time because one bad battery can damage the other. I really don't want to spend 1500 dirhams if I don't have to but I also don't want to get stranded somewhere in the summer heat because I was too cheap to replace something that should have been done. I think I need to find proper Mercedes battery installation experts Abu Dhabi who actually understand how these dual battery systems work and can tell me exactly what needs to be done without guessing or upselling. Does anyone here own a Mercedes with two batteries and have experience replacing just one versus both? How long did the other battery last afterwards? Also do both batteries need to be coded to the car like on some other European brands? Really appreciate any clarity you can provide because I'm losing sleep over this. Thank you.

Last edited by jowancox (5/11/2026 7:40 am)