According to BMW dealership the new after-market battery must be registered to the on-board computer, because, otherwise, the car would think that the old battery is still in and it would end up being charged the wrong way.
So this morning out of curiosity I decided to do a test on my friend's BMW X3 that she had been driving for a year with unregistered, after-market battery. Here is what multimeter indicated:
- In the morning before even starting the car the voltage was at 12.0V
- After starting the car the alternator started to charge battery and voltage increased to 14.0V
- I kept driving the car for 30 minutes without stopping it and the voltage across terminals was still at 14.0V (alternator was still charging it)
- Then I stopped the car and finally was able to measure the voltage of the battery and it was at 12.4V. I touched the battery and it was cold.
So where exactly is the problem with not registering battery with on-board computer? Some ideas:
- Would the car eventually stop to charge battery while it was still on if it was registered with car (i.e. readings in step #3 would have to be <14.0V)?
- Also, isn't the morning voltage of 12.0V too low (e.g. three days ago I had to jump start her car, but at that time I chalked it up to the salon fan that was on while engine was off last night.)? Maybe the battery has already started to degrade?
Update #1 Voltages were measured when it was 52 Fahrenheit degrees outside.