Modus battery draining

Sounds like a potential parasitic draw or a charging problem. Have you checked the battery voltage when the engine is off and when it's running? A healthy battery should be around 12.6V when off and about 14V when the engine is running. Also, have you added any new electrical components recently, like a new radio or lights, that could be causing the drain? A failing alternator could also cause these symptoms, not properly charging the battery while driving.

I haven't checked the exact voltages, but I'll do that. No new electrical components were added recently. If the voltage checks out, what else could it be?

If the voltage is off, investigate the alternator and battery. If the voltage checks out, then it is likely a defective battery sensor. Given the error messages and symptoms you described, plus the mileage, I would suggest getting it checked out at a workshop. They can properly diagnose the battery, charging system, and check for parasitic draws. Without proper tools, it can be difficult to pinpoint the exact cause.

Thanks for the help! Took it to the shop as you suggested. Turns out it was a defective battery sensor causing the issue. Repair cost me 315€, but at least it's sorted now.