I have a 2016 CLS 550 with 17000 miles on it. This morning it won't turn over so I had to borrow my son's Prius. Came home after work and I decided to check the voltage. The multi-meter gave me a reading of 11.6V, way below 12.5 V. Is it pretty straight forward replacing them? I replaced a couple of batteries in my life time but not Mercedes. Do I need to unhook the auxiliary battery in the trunk also? Batteries Plus quoted me for an Optima 36 months guarantee with 800 cranks Amp for $290. Only thing is that they have to special order it. Any tips will be appreciated.

 

You need a sealed AGM battery, not necessarily an Optima. I'd check places like Autozone, Advance, O'Reillys, and even Walmart. Meet or exceed the OE battery CCA. It's a common size and easy to change. You might consider taking it out and having it load tested first. Remove the Negative first and connect it last. Marv

 

Thanks Marv.

 

I forgot to say, don't go to the dealer unless they have a massive sale going on. You should be able to get on at the above places for $200ish or less. Most batteries are made by Johnson Controls (though they just changed their name and ownership) including Varta batteries which are the Mercedes OE battery.

 

Also there is the secondary battery in the trunk. I am unsure, but I believe it can also cause some issues with restart on start-stop, and I bet if it is bad it presents a weird load.