[Kylep]

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.

 

[EnvoyBoy2004]

After 5 years of service, the battery has lost its capacity. Replace the battery.

 

[Kylep]

Can a bad battery cause high voltage from the alternator?

 

[autojoe]

Gm has rvc. Can go from 11 1/2 - 15.5 volts. I have a 2008 tb. I know mine does. If there is a problem the bcm will set a code and turn mil on. Have battery load tested. If battery is old then wouldn't be bad to replace it.

 

[Kylep]

All the way up to 15.5? That’s interesting. I am definitely going to get the battery tested, I’ll probably just pick up a new one anyways since it has been having issues in this cold.

 

[autojoe]

When my tb is cold can see higher than normal charging voltage. You have the current sensor around negative battery terminal then you have rvc. I took a 2 hour course on it years ago. There's like 8 different modes.

 

[Kylep]

That’s great to know! Thank you so much for your help! The temps here have been well below zero the last week, so I guess that makes sense.

 

[autojoe]

Your welcome
I live in Pennsylvania and gets cold here in January.

 

[fade41]

Batteries last 2-4 years in Texas...

 

[SteveJL]

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.

That would make sense, since it has to use extra juice to crank when it's cold, the regulator will throw it back some extra Vs at first.
If the battery hasn't been taken out in 5 years, it might be worth cleaning the posts and connectors- and you could get another year out of it.

On the other hand- at this rate they might be 5x the price next winter