When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
Car got a new battery this spring and is suddenly charging at 15v starting and eventually settles around 14.8.
Previously on the former battery, after starting would charge around 14.8 and settle to 14.3.
Any concern to this? Not sure if this would be enough to make the battery off gas, just more concerned that it changed and seems unusually high. Resting voltage is 12.5. Alternator is original at ~120k miles. Would you suspect an alternator issue?
Are you going by the dash volt gauge or a meter right on the battery? If its holding at 14.8 no worries, but after a good cruise feel the battery and see if its warm or even hot.
I haven’t put my meter to it, so yes, by the dash but it’s a 94 so I am reading the digital volt readout on the lcd. I’ll verify with my meter next time I start the car. Imagine the battery might feel warm regardless simply from where it resides in the car.
First let the battery sit on a battery tender overnight to make sure its fully charged. It may be under charged from sitting on the store shelf and the alternator is working to bring it to a full charge.
Or it could be a connection issue. Double check your battery connections, with a small amount of resistance at the connection the regulator will see an artificially low battery voltage and raise the charging voltage.
Haven’t driven it again yet. Will mention, after I purchased the battery it sat on a Deltran tender for about a week before the car was started. So it was fully topped and shows a perfect 12.5v at rest. I’ll check the connections, I did add a quick disconnect on the negative terminal with the new battery. While I don’t suspect it, it’s easy enough to remove and eliminate.
I wonder if the voltage regulator is failing. This spring, after some work including new motor mounts, I did throw a booster on the old battery to get it started. It was stone dead on its own, once started I pulled the booster. I know that can be hard on an alternator. It ran for maybe 20 minutes total on the old battery.
It all behaves somewhat normally, higher voltage for a few minutes then settles in the 14.x range. Just never seen it at 15 till now.
Definitely check the connections first. Corrosion at the terminals can cause all sorts of issues. If all that is fine, then your alternator could be on the way out. The voltage on mine started off like that, then started swinging up and down, and got worse and worse until I smelled something fry in the alternator, and barely got it home(I was still diagnosing the issue, short test drives). I suspect one of the diodes in the alternator fried. The car still had an old battery in it too, so if the battery was bad, it could've over-stressed the alt, or vice versa. Who knows! I replaced both and now all is good again.
So in short, first check the connections, especially the positive cable, sometimes they get corrosion under the rubber sleeve. Second, have the battery tested, could have a cell or two that are toast. If all that checks out then get the alternator tested out, as it'll likely be the culprit, assuming you still see higher voltage regularly. 15V isn't too bad, but if it starts going any higher, or stays there, then there is an issue somewhere.
Last edited by novaks47; Apr 13, 2021 at 09:19 AM.
jmgtp - FYI, a fully charged battery should read 12.6-12.8V. 12.5V is not perfect, is not fully charged. And your Deltran tender puts out 1.25A (the Deltran JR = 0.75A) which will take forever to recharge a discharged battery. A battery tender is not a charger. It is meant to maintain a battery while sitting inactive, not to charge it. And a new battery does not mean it is good. Before you start throwing out money on a new alternator, you have to start at the beginning - bring your battery in for testing to an auto parts place, service station, or where you got it from. It needs to be put on a regular charger and then once fully charged, load tested. All these places will do that for free because they would like to sell you a new battery if yours is bad.
And if you have driven the car and the voltage gets up to 15V, if the battery was good, it would be fully charged after that ride.
And the first thing to do is to take apart and clean and tighten the two battery connections, that could easily be your issue if it's not the battery itself.
Only after you do that do you start looking at the voltage regulator or alternator.
keep in mind, the 12.5v I reported was on the LCD, meaning key on, engine off, there’s some draw there that would drag down the voltage when they car isn’t running
I validated things today with a digital multi meter.
12.9v key off, voltage at the battery
12.5v key on, voltage at battery
12.7v key on, voltage reported by lcd
14.75v running voltage at battery, cold start
14.9v running voltage reported by lcd
I think voltage reported at lcd may be off. This all seems within the realm of normal. Will still pull cables/clean those terminals. Also need to try it all again with the quick disconnect uninstalled.
Sounds like you're getting worked up over nothing. Clean off and tighten the battery terminal connections and stop looking for trouble, sounds pretty normal to me.
Suddenly charging at 15v
