I have a 2017 Lexus I350 F Sport. During this time where were stuck at home, my Optima Red Top died, I jumped it and it started up fine...until a left it there for a couple days. I bought a Optima charger, charged it and put the battery back in the car and the battery is at 12.9v sitting, installed with car running at the terminals shows 14.4v. I bought a OBD II sensor that shows voltage, it shows 13.7v and driving to the store and back went down to 12.9-13.0v. The car doesn't give any errors and starts up fine. I thought the car running should be in the 14v range. Im putting a Stinger AGM in tomorrow (its charging now) to see if it does the same thing. Any ideas why the voltage goes down while driving?

THX

 

Have you had the battery tested? Easy way to tell if it needs replacing. A weak battery will still start your car, until it doesn't. That's deep, I know.

 

I had AutoZone charge it and I used a Optima charger which does some other stuff to it. I am going to use a new Stinger battery tomorrow and see what happens...Its weird when running at the clamps it shows 14.4 but the OBD and my Stinger volt meter cant both be wrong. I'll post up when I try the new battery...

 

The battery charging voltage will vary based on vehicle load.
So driving you can expect it to be different than idling. Keep in mind too that you're not seeing amperage.

As an example, check the voltage when the vehicle is idling with everything off...I mean everything.
No radio, wipers, defroster, DRL (set the parking brake before starting the vehicle), headlights, seat heaters, steering wheel heater, interior lights, etc.
And then turn all those things on and check the voltage again.

If you have a battery charger that has an Amp meter on it, you'll notice when charging a dead battery the amperage is low, almost zero because it's easy to put energy into an empty vessel.
As the battery approaches full charge the Amp meter will start to rise, maybe close to 30 Amps, because now the charger is trying to stuff the energy into the battery because it's almost full, so it's working a lot harder.
The Alternator basically does the same thing for the battery when it's in the car...trying to manage charging when the vehicle is under no load all the way up to maximum load. So idling with everything off the voltage will be higher because there's no strain on the battery, so the alternator can max out the charging voltage. As soon as you turn everything on, or drive the vehicle, the load has increased exponentially and the alternator is basically playing catchup...so the voltage will not be that high like no load idling.
Based on the numbers you provided it seems like your vehicle is operating normally.

 

I didnt really think of it that way...volts to amps. I never had to check it before the battery died as I bought it in May of 18 from Lexus Of Bellevue (was the finance lady's demo with 7K on it) and replaced the stock battery with the Optima red top and JL Audio Amps/12w7AE's etc. I guess I was worried as I never checked it before . Ill check that stuff today, Thank you for that info!!!

THX