Battery Voltage

So a few weeks ago I experienced a pretty low battery and was barely able to start my truck. Turns out I had left my cargo light on for a long time and I suspect this eventually ran down the battery. My local Auto Zone charged the battery and says their test indicates the battery is good.

We have been down in Los Angeles visiting our daughter and new grand son so the truck has been sitting for 7 days. I noticed the truck was a little slow to start up again when we got back on Friday.

When I'm running the truck the battery voltage shows 14V. When I just turn on the accessory, the batt voltage gauge shows <8V. When I start the truck the gauge first shows 11V then quickly moves up to 14V.

We are heading down to Los Angeles again tomorrow so the truck will be sitting for at least another 5 days.

My truck is a 2018 RAM and this is the original battery. Even though they say the battery is "good", I'm thinking I should probably plan on replacing the battery when I get back. What is the conventional thinking here?

THanks.

Here is a pic of the Batt Voltage gauge with just the accessory on (truck not running):



Here is a pic when the truck is running:

If it was me, I would replace the battery. It sounds like you have a weak cell or two or more. The battery may be saved if it was started and driven every day and charged the way it should in normal driving. But that is no guarantee you can save it. If you drive it and then shut it off, it may be the correct voltage and start the truck as it should and pass a battery test but as it sits for a few days it loses the charge it is rated for.

I don't have a lot of faith in those digital "smart" testers that parts stores are using now.

Put an old school carbon pile tester on it and I would bet money it fails a load test miserably. Four years is a good run for modern batteries.

Before you do anything else, clean the terminals on the battery. Prob'ly 2/3 of the time that will solve problems. Also, make very sure nothing is turned on when ignition is off.....That <8v puzzles me. Maybe hook a temporary ammeter up to it ??

A similar thing I had about a year ago turned out to be the power supply for a new GPS. I left the old one plugged in all the time and just turned it off at the end of the day. When I installed a new GPS, problems started - that power supply would drain the battery. I know it's solid state and shouldn't do that.....but it did.

Wet cell? Not cleaned off peridocially or keeping electrolyte levels up there? If so, with a battery where the plates have 'sulfated', i.e., are now compromised, the remaining plates may charge and read ~12.6 volts or so ... leaving you to think it is 'OK', but there's no oooooomph, power or amps behind that voltage.

I'd buy an Interstate or NAPA commercial battery, if they make one to fit your vehicle.

Thanks everyone.

The terminals are in pristine condition and are treated with that grease anti-corrosion stuff. I should probably use some of that stuff on the boat batteries.

Other than the cargo light, which was probably on for a long time due to my mistake, I don't see any other accessory that might cause a drain and I haven't added anything.

All I can tell you is the original is a large sealed battery (Group 49?). I had no luck with a match from the local Interstate dealer. So far, I can get a Duralast brand from Auto Zone or Napa's Legend brand. Both are AGM and fit my truck. Can't get a fit on Napa's Commercial brand.

I think, if it were me, I'd spend the $30-$40 on a battery tender/trickle charger to take with me. Plug that in at the distant destination and call it good. Delay having to lay out the coin for a new battery for awhile. You do, after all, live in a much more temporate climate than many of us.

Just thinking like a cheapskate.....Roger

Do you have or have access to a hydrometer to check the condition (specific gravity) or assessment of the electrolyte? Electronic checkers are marginal in this regard as they only show voltage 'potential' (but not power). Meaning a 12V battery that tests 12.X on a electric test might show low on the electrolyte scale, proving a cell is damaged. That can be tested by checking each cell.

Not that I'd get this $10 one, but you get the picture ...

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DaleH said:

Do you have or have access to a hydrometer to check the condition (specific gravity) or assessment of the electrolyte? Electronic checkers are marginal in this regard as they only show voltage 'potential' (but not power). Meaning a 12V battery that tests 12.X on a electric test might show low on the electrolyte scale, proving a cell is damaged. That can be tested by checking each cell.

Not that I'd get this $10 one, but you get the picture ...

Click to expand...

HiYa DaleH. It is a sealed battery.

I'm heading home this Friday. It will be interesting to see if the truck fires right up or struggles.