mac911

My 2008 C300 is starting VERY slowly. So much in fact, I'm not going to drive it again until I get the battery replaced.

I was going to put a 94R AGM battery in it, perfect fit, same case on the battery as OEM too. However, with some research, despite all the AGM and VRLA talk here, I have found the W204 probably doesn't have AGM or VRLA batteries, do you agree?

The reason being is AGM batteries should typically never be installed the engine compartment. They do not like heat, indeed charging typically needs to stop around 120F. Furthermore, if the car isn't coded form the factory for AGM, it will charge it slightly too much and overtime, hurt the battery. AGM charging needs to be slightly lower from what I have read. This is why BMW wants the car coded to the battery type, so that it can charge correctly.

Furthermore, I took the air box cover off my battery, and I see no mention of VRLA or AGM. It even has the acid window, and I don't think it would have that on a AGM battery where acid is absorbed in the fiber glass.

On the other hand, Mercedes where the battery is under the seat or trunk, have AGM batteries as they put off less gas (safety) and they stay cooler in those environments.

Therefore, I'm thinking I need to go with a regular flooded battery? I would get OEM dealer battery, but don't really have the time to make the extra driver there, 3x further than my nearest parts store.

Thanks for sharing any experience you have with this!

steveb9771

Call Mercedes roadside assistance. They will come to you and check your battery. If it needs replacing, they will have one with them and install it. The cost should be the same that you would pay if you went to a dealer.