Bad batteries?

This is the kind of tester I have. My batteries all tested OK. Well just OK. I had 4 of the 750's they wouldn't hold a charge more than a day.
I put three 1050 CCA batteries in and they seem to do the job. I will get a fourth when I get back to the shop. They only had 3 when I needed them. $99 each. Not a bad price. Ameristar. Looks just like the Northern brand.

 

Disconnecting battery cables with the engine running was one thing I was told would 9/10 times kill the diodes in the voltage regulator. I've never been brave enough to try it myself though so I can't confirm it.

 

That cable disconnect was a standard test, by the book, for Motorcraft products years ago and possibly others. I would just be concerned about electronics damage due to voltage spikes and I do not know if all brands of truck alternators work that way.

 

Yes, it is possible for an alternator to put out 14 volts and very little amperage. Its kind of hard to explain how an alternator works but if a diode in the regulator shorts or becomes open, you can lose between 30% and 70% of amperage output.

Another thing not to rule out is poor connections and cables in the charge circuit. You could be seeing 14 volts at alternator but your batteries might only be seeing 10 (as an example).

 

I never knew that. Almost every mechanic I've ever worked with told me that was a big no-no. Learn something every day.

 

I'm so old and old school that the thought of doing that makes me cringe enough never to try it on mine but I'm old and cranky enough to watch someone else do it on theirs .

 

It is with modern vehicles

 

Well dang guys/gals. Guess I best not check my batteries that way any more.
What do you mean by "modern".
Thanks for the update.

 

Anything with a computer. Maybe any thing with an electronic voltage regulator which Delco went to in 1987. Anything you put a refrigerator in because it probably has a circuit board in it. Saw gauge panels, resistors and or diodes, cooked in 9670's when jump started with a welder. My understanding is the voltage spike can get the electronics. Sometimes they are very reziliant to welding on the frame, jump starting etc., the next time a battery cable ark can cause a problem.

 

Hi, I need some help diagnosing the charging issue in my truck. I have a 2015 Volvo.

I bought and installed new Exide-red-top batteries just last week and they already went down below the charge level, where the battery protection system kicks in (cutting off interior power to prevent batteries from draining) 3 times within just 30 min of using interrior lighting (after day long driving each time).

The charge guage in my instrument cluster is showing between 13.6 to 14.2 while the engine is running, it goes up and down constantly (not very fast, but it changes).

I also noticed that sometimes backlight on my instrument cluster’s lcd is pulsing - not sure if this is connected to the issue.

Old batteries were replaced, bc one was cracked and they also didn’t hold charge for long (but I never tested them).

All those symptoms were also present on old batteries, it’s like nothing has changed with new ones. The only difference is that now, even after this power drainage system cuts off, truck starts easily. On old batteries when it happened it was struggling to crank.

Thanks in advance for ideas guys.