Battery help : AGM

Just replaced my alt last night took a crap on me. Thinking should I replace both my agm batteries idk if there bad or not. They where both replaced with the alt 4 years ago. When I drive my voltage read 14.4 solid while driving reg. If I come to a dead stop it will drop to 13.8. Then go back up to 14.5 back to a steady 14.4. Any help please thankyou.

 

Most parts stores test batteries and charging systems for free. You could get it checked and decide from there

 

Measuring voltage while running just confirms your alternator is good. You should be at 14v +/- with the engine running.

You need a battery tester to test the batteries. I have a cheap one that measures cranking amps, capacity, etc and gives you a rating based on that, but any parts store will usually have one and test for free.

 

1 battery good and one was fairly discharged

 

Your terminals aren’t covered with acid boogers?

If you have a multimeter you could do a starter voltage drop test. Simply hook to the battery positive to positive negative to negative, set to dc voltage. Better meters have peak high and peak low hold functions. If yours has it, set to peak low. If yours doesn’t have it, you can still test, it’s just not as accurate. Start it, it’ll record what the battery voltage drops to. Since you have 2 batteries, do the same on each. 10.2 - 10 is getting iffy. Less than 10 is a candidate for replacing.

Parts stores are in the business to sell you parts. Not to test your battery, say it’s good, and send you on your way. Maybe that’s why my battery tester fails everything except brand new batteries.

 

https://www.tacomaworld.com/threads/the-northstar-agm-battery-voltage-booster-upgrade.604478/

 

Wait, your alternator only lasted 4 years? Oem Toyota?

 

Napa brand.. lifetime warranty

 

Noo looked cleann