My 05 envoy xl 4.2 battery was having a hard time starting the car this morning, it was -9 out with windchills down to about -20. I jumped it and it started just fine so i decided to check the voltage of the alternator and it was reading at just over 15 volts, after I let it run for a little bit it dropped down to about 14.7. Should I be worried about that? Also could the battery be causing the high voltage when it’s that cold? The battery is about 5 years old so it probably wouldn’t hurt to get it tested anyways.