Charging voltage dropping - is this normal or a problem?

[Gary Bailey]

I have a (new to me) '06 Sierra - in my work it spends a lot of time idling with little or no electrical load (parking lights only). When I first start up, and on short journeys, the battery voltage goes up to 14.5 - 15V every time, however I've noticed that when it's been idling for a while (30-40 minutes with short moves every 5 minutes or so) that voltage drops to 13-13.5V - if I shut off and restart the engine, it goes back up to 14.5V+ - and the following day it's right back up to 14.5V - 15V

 

I'm not seeing any other electrical issues (lights stay bright, always starts well, passed the charging test at NTB) so my question is whether this is normal as the battery approaches full charge or if this is a symptom of a problem brewing?

 

Thanks!

[Eric D Plante]

Hi Gary,

I think it is normal. When you restart the truck you draw off the battery, and it needs to recharge because of this. Of course as you sit idling for a while it can recharge the battery and then the load is less on the alternator. I'd still keep an eye on it but prob just normal.

[00Silverado4x4]

That's completely normal. GM has used an on demand type charging system for several years now. The battery will charge up and then the alternator will essentially "turn off" and then once the voltage drops down far enough the alternator will "turn on" again and charge again.

[sahls01gmc]

Yup, my 2012 Traverse does the same thing. At first, I thought it was an issue when the battery gauge went down to 12v. But it cycles on and off a lot. Time will tell, but the theory seems like a good idea in the sense that it won't constantly be charging which could prolong the life of the alternator and battery.

[Gary Bailey]

Thanks all for your responses - much appreciated! Happy Thanksgiving!