Anyone running a lightweigh battery on 3.0si?

[Novel]

Hi,

I've recently had an unsuccessful attempt installing a lightweight battery into my 3.0si E86. Currently I'm running the Varta 74Ah battery and had zero issues with that in ~1.5 years I own the car.

I've decided to try a lighter battery, specifically, LithiumNEXT TRACK60. As this battery is positioned as an alternative to an AGM 60Ah battery, and I can see that Z4 optionally had even the normal 55Ah battery, I thought that it would be good enough.

I've installed the battery, car starts just fine with it, but as soon as I start driving and push the pedal more enthusiastically, it starts turning off due to overvoltage protection (its max value is 15.2V). And I can see values around 16-17V for short periods of time. This is obviously a bad situation as the car starts behaving really weird with this intermittent battery cutoffs.

My first thought was to replace the voltage regulator. I've bought a new Bosch voltage regulator and replaced the old one. Nothing's changed.

I've reached to LithiumNEXT support for advise, and they've recommended to replace the complete alternator. I've replaced the alternator with the refurbished Bosch part. Nothing's changed.

Needless to say, as soon as I returned the old Varta battery, all the issues go away. I know that the reburb alternator is probably not the cleanest way to test things, though it seems quite unlikely that it's the problem (as basically I've tested 3 different voltage regulators: my original one, the new Bosch, and a complete alternator assembly).

At this point the support has nothing to suggest.

So I'm wondering if anyone has real experience running an LiFePO4 battery in N52 E85/E86?