stan1024

Hello all, I am a new member here and am looking for some help. I recently purchased a 2015 S550 4matic and I’m having a starting issue. When you go to start the car it has a weak start. After driving either short or longer period it will turn over but not start. The sign it shows are of a dead battery. After trying to start 2-3 times it will not turn over at all. I connect a jump pack to the front under the hood terminals and the car starts up. I went to a MB dealer and bought both the H9 battery and the auxiliary battery and replaced them. I went to start the car and still it has a weak start. Not sure if it can be the starter being that it starts with the jump pack. Has anyone encountered the same issue?

MBGuy2022

Sounds like a bad connection at the main battery terminals. Was there any corrosion at the terminals? Where they cleaned properly before being reinstalled? Is the new battery fully charged? Mine came half charged.
My Aux battery had bad corrosion at one of the terminals when I replaced mine.

stan1024

the battery terminals did not have any corrosion but they were still cleaned. My mechanic connected a battery tester onto the old main battery and it showed the battery was good. I was able to return the new battery to the dealer and so I did that and put the old one back on. The auxiliary battery showed weak so I did put the new one and kept it in. I am now thinking of the new battery was not fully charged. The manufacturer sticker on it was from November of last year and my original battery is only 2 and a half years old. The auxiliary battery terminals were in good shape also. And slightly brushed with a wire brush. I am wondering if it could be the power cable that goes to the starter.

TripleDown

Invest in a good battery changer so you can get both up to 100% before you replace anything else. Having a good charger is something you will always be glad you have on the shelf.