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02-24-2019
I have a 2006 Grand prix base model with a new battery I put in back in November. Intermittently the car simply will not turn over, so I get it boosted, the car is fine for a while, then it won't start again...rinse and repeat. Today I put a battery tester on the battery and it showed 12.7 volts not running and 16 volts running. The battery is being overcharged obviously, but why? and how can I test to see if its the voltage regulator or something else.
Scottydoggs disliked this post
02-24-2019
the alt could be bad. ive had 2 in a row rebuilt's for a truck i owned over charge, truck hated it too. so much it told me so on the DIC lol
02-24-2019
volts don't start a car... amps do. While you appear to be having a volt issue, what do the amps say?
02-25-2019
You have a kind of scatter shot mess of information here. A car that won't turn over isn't always a low battery, it could just be a bad connection at the battery, or a bad starter, or a bad connection at the starter..
Next time it won't turn over, check your battery voltage directly at the posts. If its anywhere above 12.2, its just a loose connection or bad starter.
When the battery is low, the alternator will put out more voltage, at least the one in my truck does this when i leave it parked for several days.
Then when the battery is well charged, the charging voltage drops to ~14V
So in your case, intermittent charging (or possibly a constant load drawing down the battery when it is parked) puts the battery in a weak state and the alternator pumps out more juice to bring the battery back.
If you have a charger, Charge the battery up well, then re-test the alternator charging voltage.
THe battery reading @ 12.7 is fully charged..
EdIT:
3 month old battery means this has probably been an ongoing issue? or maybe the battery change created the problem?
Either way, often times batteries go dead because the alternator is on its way out.
the old alternator in my truck had deep grooves worn in the contact rings and brushes that were worn too short to make full time contact.
I would notice my headlights going from normal brightness to dim randomly when parked with my headlights pointed at a wall
Last edited by Cerberus; 02-25-2019 at 02:48 AM.
03-02-2019
Thanks guys for the responses, I'm 90% sure now that all this trouble is caused simply by bad battery connections, but there is a but!!! With the engine running I put a battery tester on the posts it shows only 12.7v, when I put the tester on the connectors it show 14.7, BUT...as the Battery tester stays on the connectors the volts slowly go up past 15v towards 16v, which is why I initially asked about the battery overcharging. My question is would the alternator put out more volts than normal 14.7 because there is a bad or no connection to the battery posts??
03-03-2019
if you are reading 12.7 at the posts with the engine running but 14+ at the connectors, yes, you have bad connections.
remove connections and clean up mating surfaces with a battery terminal cleaner brush. Clean battery posts too.
butter both up with a dielectric grease (I've also seen white lithium grease used)
reconnect and retest
report back here
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