Mini Roadster Rear Window Heating Issue

I had a similar heating issue with my Mini Cooper S. The rear defroster and windshield heating acting up simultaneously is a strong indicator. Have you checked the battery's resting voltage and load capacity? A heavily discharged or defective battery can cause all sorts of electrical gremlins in these cars. The heating coil requires a stable voltage to function correctly, and a weak battery can't provide that, especially under load. Further complicating matters, the car's computer might throw error codes due to the voltage fluctuations, which aren't always directly related to the heating system itself. Start with the battery diagnostics. If that checks out, then you'll need to delve deeper into the heating system's wiring and relays.

Battery state seems plausible. What voltage drop did you observe with your Cooper S during rear defroster activation?

I did not measure the exact voltage drop, however, symptoms match your description precisely, including the error memory entries. Given that you suspect the battery and similar issues are known, I recommend a workshop visit. They can perform a proper load test and diagnose it accurately. Messing with the electrics on these cars without proper tools and knowledge can be a costly mistake.

Confirmed. New battery installed; thermal window heating and auto defrost now operational. Total damage 290€. Thanks for the input.