Changing the battery of BMW F30 — AGM to Lead Acid

As a first-time premium car owner, especially a used car owner, I was a little worried about the expenses the car can bring in. And there I was right after 2 weeks of the purchase finding out that the battery is dead. Of course, the dealer didn't want to fix it for me and I was on my own.

I checked with BMW service and they said a whooping 43k INR (which is like 580 USD) for the battery. I was quite surprised by that. I did some research and figured out that they use AGM (Absorbent Glass Matt) batteries imported from Germany. It's a 90Ah battery.

They said we cannot change it with a usual battery in the car and it needs to be registered in the ECU. I didn’t want to pay such an amount especially right after purchase. I did the research and found why they prefer AGMs. The chances of fumes coming out from the battery is less and also there is vent to let any of such gases pass in these batteries. Also the batteries doesn’t spill any acid. It also has better life they say and charge storage capacity. The first 2 points made more sense for the battery being in the trunk of the car, but I believe the modern closed maintenance-free batteries doesn't release that much fumes or they can ever spill in a normal operation. So I decided to go with such a battery.

I approached Mustang Motors and they said they have Bosch battery in stock and they assured me that it's fine to use it. It was a 100Ah battery and I was happy with it. It was around 17000 INR for the battery. I was still doubtful why the car needs it registered. I learned that the charging pattern the car uses for a new battery and old battery is different to increase its life and also reduce the unnecessary use of the alternator (which in turn adds some load to the engine and there by reducing the mileage by some fractions). That was understandable, but the Mustang guys didn’t say anything about changing the battery type. I was thinking, if the new battery needs registration, probably a battery type change also needs to be fed into the car.

The research led me to the app Bimmerlink and Bimmercode developed by a German company which can be used to code the car to unlock certain features that the car does not come with. I will write another article explaining it. But this app had the option to set the battery type. I told the Mustang guys that I will register the battery myself. I did change the battery type in my car from 90Ah AGM to 90Ah (which means a normal battery) and coded it into the ECU using Bimmercode. Then I registered it as a new battery. Now my car knows that its a non-AGM battery (so it can adjust the charging pattern appropriately) and also its a new one.

A lot of confusions and thinking went into this process but in the end, I am happy with what I learned and fixed. I am writing this, because if you cannot find a concrete answer to this question of changing to a non-AGM battery — there is a solution. If you are in Kochi, I would be happy to help. You dont need to spend money on the paid apps like Bimmercode/Bimmerlink.

See you in my next article.