I have plugged the car back in. Before I did so, I measured voltage at the battery, and as you noted in a different thread, as soon as you unlock/open a door, it starts attempting to run the DC-DC system, applying 14.8V to the battery. Plugged in, it measures the same. I opened up bimmerlink, and watched the battery state go to 99%, where it remains stuck - I do not think it will ever read 100%. The DC-DC system continues to shove out 14.6+V. This is charging with doors locked. The battery first gets hot on one side, then gets hot all over as it is having quite a bit of current pushed through it, with no chemical reaction to make since the battery is fully charged, it will only make 100's (or 1000's) of watts of heat inside the battery. The sulfur smell is accumulating again. Though not as strong as when it had been charging for hours, I am not going to let it build up that much again, so I opened the garage while I continue testing. Now even with the door opened, the smell is getting stronger. This is not surprising because the i3 is applying rapid charging voltage to a fully charged battery.
I am now 100% certain the i3 is recklessly charging the 12v battery. The i3 is treating it's 12v system like an ICE vehicle driving down the road at half throttle and load, in every situation the DC-DC system is on. Even with a fully charged 12v battery. This is a dangerous problem. This is an obvious programming defect and should be remedied for safety.
For comparison, I hooked up a basic battery charger to my 750 - also an BMW AGM 12v battery. It read the battery at 12.4V, 63% charge state. It began charging at 12.6V and slowly increased the voltage to 13.5V. As the battery warms and cools, the voltage fluctuates between 13.0 and 13.5. This is proper charging of a battery. What the i3 is doing (at least in model year 2016) is not.
These batteries are meant to have a service life of 10 years, so it astounds me to see people saying just replace it and move on. It should be obvious there is a problem.
What I am now curious about: will replacing the battery cause the charging system to behave differently? Is it in some sort of fail-state where it thinks it needs to pump out 14.6V to keep electronics going without a good 12 battery? Or does the system always charge like this and slowly ruin batteries for people who charge every day?
