Battery voltage 14.5V & 15.6V - too high??

Hey TW, happy Saturday!!

My 2018 Tacoma was having some trouble starting (engine wouldn't turn over), so I checked the batteries. The starter battery (OEM) was at 14.5V and my aux battery was at 15.6V (which charges from the alternator through a BlueSea ML-ACR). I don't check my batteries often, but I can't remember ever seeing the voltages this high. Is it too high?

Oddly when I tried to start the car again, it turned over no problem.

Thanks
Andrew

 

That does sound a little odd. Usually, the charge of a resting 12V battery is around 12VDC. It might read more when the alternator is going.... you got anything else providing power like a solar panel?

 

No other power sources; just the alternator. I'll check in a couple hours and see if it has settled down at all. Seems really high to me.

Should I put a load on the battery to truck 'suck' some of the over-charge out?

 

Try putting a load on it and testing it. Maybe turn on the headlights with the engine off and test.

 

Seems it's getting overcharged which could lead to premature battery failure. I would definitely inspect the battery and have a shop test the your voltage regulator isn't faulty.

 

A fully charged battery at rest should read 12.8 volts. A properly working charging system should top out at 14.4 to 14.6 volts. Charging to 15 is murder on a battery. Heat destroys batteries not cold. Cranking in the cold takes more juice. Your battery will be trash after the summer. First cold day... Click click click

 

I'd check the charging system and see what you are getting. I'm not completely familiar with Toyotas, but your regulator might be bad.

 

14.5 would be proper charge voltage from your alternator.. when its not actively running/charging it should be around 12.4-12.8 if the voltage drops below 11.8 when engine is off your battery is getting weak.. you should have it load tested.. the 15.6 is beacuse your charge controller is not reading battery voltage correctly.. it should stop around 14.8 MAX.. dissconnect the bluesea controller and test the battery.. if it checks out to around 12v-13v.. it should be fine.. the charge controller should switch off, or dump to a dummy load (typically a coil, or incandecent bulb arrangement)

 

The assumption is that your voltmeter is accurate. Have you tested it on another vehicle? In my experience, 14.3V would be top charge voltage. Certainly anything more than 15V would be defective.

 

I can't see how using an ML-ACR you can get this. It's only connecting batteries together so if the main is 14.5V then the aux has to be that or lower. Or perhaps you have a perpetual motion machine charging the aux?

 

I checked this morning, with the engine off and ML-ACR in the off position: starter = 12.93V and aux = 16.20V (still way too high).

I'll leave the charging relay off for now, and have put a small load on the aux battery to try bring it down to 12-13V.

 

Check your meter. I've got a Dodge Cummins and had an issue causing the truck to stop. Mine was a loose connection from the ECM to the battery ground at a battery terminal. At the same time I decided to check voltage on my batteries and got high readings of around 16V.

I changed the 9V battery on my meter and brought everything back to normal.

 

Just a thought before you start changing anything. Try a different meter to make sure yours us reading correctly. If you dont have another meter, try yours on another vehicle to see if it also reads high? Just a thought.

 

How long have you had this dual battery setup? They are setup in parallel, not series right?

 

You guys were spot on. Replaced the 9V battery in my voltmeter and started getting much more realistic readings! Thanks for your help

Aux = 12.9V and Starter = 10V ... looks like I need a new starter battery (which explains the engine not starting in the first post). One of the benefits of having an aux battery you can easily connect to the starter when you're in trouble.

 

Well just glad that's all it was and an easy fix.