This past weekend I replaced the battery on my 2006 BMW M3. It wasn’t holding a charge well and struggled to start the car. The battery was over six years old, so it was time for a new one.
My E46 M3 is the last generation of BMWs on which this is still a simple DIY operation. Newer BMWs have an “intelligent” electrical system that requires a new battery be “registered” with the car’s electrical system for proper charging. This requires a computer, either at a dealership or a well equipped independent shop.
As usual with these cars, there are plenty of options and opinions on the best battery to get. It doesn’t make sense to pay a premium for a BMW battery. BMW switched suppliers about 15 years ago, and most car batteries are more or less the same. I talked in detail about this in 2012, when I replaced my E36 M3 battery.
I’ve had good experiences with Interstate batteries. So I went with the MTP-94R H7, which was almost a perfect match in size. My favorite local shop didn’t have it in stock, so I bought from NTB. Got what I think was a good price, which included a $20 core charge refund for my old battery.
I ran into one complication during the install. Since the battery is in the trunk, BMW batteries require a vent tube for gases to escape. Whoever installed the current battery had sloppily shoved the vent tube directly into the side of the battery. This had pinched off the end of the tube, and I doubt much if any gas was being vented.
There is a small, black elbow piece that connects the vent tube to the battery. I had made sure I got a new one with the new battery, in case I needed it. I used a small allen wrench to open up the end of the tube, and installed it properly with the new battery.
BMW did make one thing easier on the E46 when replacing the battery. On my E36, when you changed the battery you lost all settings and battery function. You then needed to re-initialize the radio with its original code, which subsequent owners may or may not have received when they bought the car. You could plug a 9 volt battery into the lighter socket to prevent total radio loss – see the 2012 post for more detail.
For my E46, I only had to reset date and time. This was a very basic but satisfying DIY, and the car should be set on the battery front for a few years at least.
Here’s a very thorough video from YouTube publisher mypcblewup on BMW E46 M3 battery replacement, and a few pictures from my install. Note — I did not use a power drill, overkill on this job. And using a drill could easily cause you to overtighten the 10mm battery terminal bolts.
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