2009 G37x Coupe with an electrical issue that has been going on for several years, seems to get worse in the winter. Battery appears to lose it's charge. First thing I did was replace the battery (2022). That seemed to help. When it happened again the garage put in a refurbished alternator (2022) and cleaned the terminals. Issue started again nine months later as the temp started to drop. Put in another high quality refurbished alternator (Jan 2023).

Oct 2023 the car died while driving in the rain. Complete shutdown, no power at all. Had to roll the car into the garage. A couple days later they charged the battery and tested alternator. Everything looked good, recommended replacing alternator. Brought the car to where the alternator was installed and they tested everything and couldn't find any issues. Suggested replacing the battery, but I held off given that it was only a year old (at the time). Now when I floor the throttle the battery light comes on at peak RPMs along with another red light on the dash that looks like (!). The attached image shows the two lights on. Things I've done since are:

- Full battery test at garage (no issues reported)
- Replaced alternator belt and tensioner
- Replaced loose battery connector on negative wire
- Replaced Green wire due to corrosion
- No AC current detected, which indicates that the diode is working
- Left the car sitting for 2 weeks, battery voltage remained above 12.4, however it did die after a month in the peak of Canadian winter

What is really weird though is that the voltage running across the terminals is 15+ when the car is in idle and doesn't really drop???

Haven't really driven the car since Nov. as I've lost confidence in it.

I've run out of ideas or tests. Any suggestions?