Batteries load tested ok but voltage dropping

[jwalterus]

After driving about 3 miles and sitting 10 minutes off, it shows 12.8v on the meter .

Normal.
Your batteries are weak, your cables are bad, or your starter is shot (put a clamp meter on it to see amp draw when cranking).
Pick one, but I'd bet on the batteries, when they tested them, they should have told you "this one has *** CCA, and this one has *** CCA".
Remember, 70% of rated capacity is considered "good" on a pass/fail battery capacity test.
That's only 595 CCA on your 850 CCA battery.

 

[Cubey]

Yeah he didn't tell me the cca it showed. He just said they were "good".

I'm guessing it's batteries. The sudden problem was after they probably froze then had to start the truck after sitting 8-9 days and trying to start in 31 degree ambient temperature after a 22 degree low.

Seems less likely that the cables would suddenly be the problem. The starter is about a year and a half old so it's less likely to be the problem. I'll see about getting them tested elsewhere later this week.

 

[Thewespaul]

Just to rule them out you can disconnect the wiring from the alt while you have it sit and see if it makes a difference. I’d say the unknown age batteries are probably the most suspect

 

[Cubey]

I'll try just disconnecting the negative terminals tomorrow after I get to my next destination, where I'll be for three nights. I'll know if they dropped any by Saturday.

 

[Cubey]

The date code stickers are both L6, so either November or December 2016 depending on if it's Deka or Crown. Either way, just shy of two years old.

 

[retiredinhomer]

can you check the cells for water level?

 

[Cubey]

can you check the cells for water level?

Unfortunately not. It's thos awful flat top kind. Id have to break into it. Check back in the thread for a picture.

 

[79jasper]

I've had those in the past.
I think its glued on.

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[Cubey]

I've had those in the past.
I think its glued on.

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Yeah I broke into a deep cycle one once and found it severely low. Problem is trying to keep the cover on afterwards.

 

[retiredinhomer]

Unfortunately not. It's thos awful flat top kind. Id have to break into it. Check back in the thread for a picture.

I am sorry I did not run through all the posts. I paid 30 bucks extra in Alaska for a battery with caps. Without a way to check level of liquid . And voltage is ok then check discharge rate. If liquid level is low- battery will charge quickly but will discharge quickly under load like headlights on.

 

[Cubey]

I am sorry I did not run through all the posts. I paid 30 bucks extra in Alaska for a battery with caps. Without a way to check level of liquid . And voltage is ok then check discharge rate. If liquid level is low- battery will charge quickly but will discharge quickly under load like headlights on.

These are more expensive ones compared to Walmart, yet Walmart ones have removable caps. Go figure.

I guess I'll see how they are in the coming cold months. I'm charging them while both hooked to the truck with a 1.5A black and decker smart charger that I already have.

True or not? I was told an alternator only charges about 3/4 of the way and you should always externally charge if they get low.

I cleaned up the primary battery postive terminal a lot, it had dull grey corrosion. It took quite a lot with my cheap little battery terminal brush. Also double checked the other three, plus recleaned the battery rminals themselves.

 

[The_Josh_Bear]

True or not? I was told an alternator only charges about 3/4 of the way and you should always externally charge if they get low.

Definitely Not. The alternator charges them all the way. The only thing I've come across on that topic is that its healthier for the batteries if you charge them with a charger after they have been discharged, but I don't know how much i believe that. Maybe its true to some degree but it's not very often that we have that luxury anyway, in my experience. Usually its booster cables and vrrrooom!

 

[Cubey]

It's probably safe to say it's the batteries. I guess they just didn't last in this truck.

If fully charged (12.8v), one cycle of the glow plugs drops them to 12.0-12.1v without cranking it.

I do have a cheap electric fuel pump but I doubt that's the problem. It wouldn't be pulling glow plug types of amps suddenly, I wouldn't think.

Maybe the batteries just suffered from the bad alternator and glow plugs (excessive cranking) last year.

I think they are 3 year free replacement but I can't claim it, they were in the truck when I got it and I have no receipt. Plus O'reillys testers say they are good.

If they become nearly impossible to use in a couple months, I'll replace then I guess.

 

[IDIBRONCO]

It's probably safe to say it's the batteries. I guess they just didn't last in this truck.

If fully charged (12.8v), one cycle of the glow plugs drops them to 12.0-12.1v without cranking it.

I do have a cheap electric fuel pump but I doubt that's the problem. It wouldn't be pulling glow plug types of amps suddenly, I wouldn't think.

Maybe the batteries just suffered from the bad alternator and glow plugs (excessive cranking) last year.

I think they are 3 year free replacement but I can't claim it, they were in the truck when I got it and I have no receipt. Plus O'reillys testers say they are good.

If they become nearly impossible to use in a couple months, I'll replace then I guess.

Well that certainly sucks. Unfortunately, we do need them.

 

[jwalterus]

I think they are 3 year free replacement but I can't claim it, they were in the truck when I got it and I have no receipt.

Should be able to warranty them off of the manufacturer's code, I used to do it regularly, I'd pick up a battery at the junk yard (reading the date codes to make sure it was still in warranty, mostly interstate and delcos), and if it crapped out, I'd take it in and have it warrantied.

Plus O'reillys testers say they are good.

There are ways to kill the cells, NaCl for one..... I don't turn in cores anymore, I kill the cells completely, neutralize the acid, and use the lead for casting.....
If you truly want to test the batteries, you need a carbon pile load tester (old school), crank that pig over and watch it fail.

I have a personal issue with certain places, because of certain practices at retailers (certain battery testing procedures are designed to force a weak battery to pass), I don't buy batteries except for AC Delco or else I pick up Caterpillar batteries from work.