I've often read the term pre-tune checklist on various posts across facebook groups, forums, etc. One of the items that you may want to consider is replacing your Mercedes battery, regardless of how it tests if it is over six years old. There are two batteries on many late model Mercedes. This article is about changing the main battery, if you would like to see more about changing the auxiliary battery on a Mercedes, please see here.
DIY Ease Score 2-3
(out of 10 being like a re-timing/transmission rebuild, something possible but perhaps hard for DIY)
10mm socket plus 6 inch plus extension.
Why Replace a Good Old Battery?
Replacing your an older Mercedes Verta battery is important for many reason I don't understand. However, in general modern cars use a lot of electrical load for the amount of voltage they were designed for and they are very sensitive to having a working voltage that they like. And while they may crank and run a variety of mercedes elecrtical sub systems may not work optimally if the presented voltage is on the low side of what is anticipated. If the alternator is struggling to charge an older battery it is entirely possible that under the increased stress of a tune may present errors with injectors and spark plugs as well as ECU and TCU, etc.
What did I just write?
On my range rovers lots of weird little electrical gremlins were actually the beginning of being able to tell a battery was going. And it is still true today. Often things like the radio may not seem to have as much head room, or perhaps brakes feel squashy, HOLD doesn't engage as well. Things like that.
H8 Upgraded Battery Size installed into a Mercedes C218. >10% Increased Capacity
Updating the battery isn't very difficult. You will most likely need a 6" extension, a 10mm socket and a 13mm socket as well as a towel.
The battery slots in one direction which needs to be matched. The batteries themselves are slightly heavier than expected. Make sure your hood is open beyond the normal opening, but to the often available on Mercedes, service opening straight up position.
My car felt better right away. For example changing the battery provided a
Updating a battery, for whatever reason, in my car made the brakes feel much tighter with more consistent pedal feel, earlier.
This is just an example I would guess of the change of running on a 7 year old battery to hopefully something newer.