Group 31 950 CCA issues

[HenrytheHumvee]

Good evening all,

I recently had an issue with my M998 not wanting to start. I pulled out my volt meter and across one battery it said 11 volts and the other 13 volts for a combined of 24 volts. Both batteries were manufactured 06/23. It was not enough to turn the vehicle over but it was able to be jumped easily. While the vehicle was running I had a reading of 27 volts. I took both batteries into my local AutoZone to be tested and one came back as a failure, and the other passed. I looked at replacing both batteries and asked the associate to test their shelf batteries before I paid. All three of their batteries failed. I left and went to another parts store (O'Reilly's) I had them test my batteries again with similar results. they had two of their brand batteries, those two failed also. Finally I ended up at advanced and they had two batteries in stock manufactured in 12/23 and 01/24, wouldn't you know it neither of them passed the CCA test. The voltage came back fine but the CCA was 113/950. My bad battery had more CCA than their one manufactured in January. Finally another advanced store had two in stock that they tested and say they are good and I pick them up Monday. We will see if they actually work.

Is anyone else having issues with finding group 31 batteries that aren't failing right off the shelf? Is it a bad production run? What could cause this?

 

[juanprado]

Group 31 is a commercial hd battery with no automotive or light truck applications.
Advance, Auto zone, o'reilly are all auto parts.
Napa, truck pro, Farm store will all have fresh stock.

24 group all day long at auto stores and plenty enough cca and fit lower if you don't have a hd store close by.

Btw, I would not have tried to start with one bat at 11v. Sure way to get magic smoke to release from the finicky hmmwv electronics that are big $

 

[HenrytheHumvee]

Group 31 is a commercial hd battery with no automotive or light truck applications.
Advance, Auto zone, o'reilly are all auto parts.
Napa, truck pro, Farm store will all have fresh stock.

24 group all day long at auto stores and plenty enough cca and fit lower if you don't have a hd store close by.

Btw, I would not have tried to start with one bat at 11v. Sure way to get magic smoke to release from the finicky hmmwv electronics that are big $

I appreciate the advice.

 

[Mogman]

How did the group 31 batteries fit?, at first glance they look too tall.
Interstate is another good place to get group 31 batteries, we have an area/regional dist. in CC so they always have a good fresh supply, see if there is one in your area.
As HenrytheHumvee said group 24s work fine.

 

[HenrytheHumvee]

How did the group 31 batteries fit?, at first glance they look too tall.
Interstate is another good place to get group 31 batteries, we have an area/regional dist. in CC so they always have a good fresh supply, see if there is one in your area.
As HenrytheHumvee said group 24s work fine.

I actually bought the M998 in November of 23 and those were the batteries that were in it. They seem to fit fine. Like I mentioned both batteries were manufactured in 06/23 so I was surprised one was starting to go already. I plan to install a 24/12 DC/DC inverter for some 12 volt accessories.

 

[Coug]

Typically it's the forward battery that overcharges and rear battery undercharges. First in series charges more than later in series. Plus, no two batteries are ever perfectly identical to begin with, so usual recommendation is either install some sort of battery balancer, or swap the battery positions every month or so in order for them to take turns in each position.
Other option is to us 12V chargers on each battery individually every month or so to bring them up to an equal state of charge.

27V while running sounds like an alternator issue that needs corrected. Even with a bad battery, the alternator should be pushing 28V. Anything less won't properly charge up lead acid batteries.

As for the battery failures, it wouldn't surprise me in the slightest if every single one of those batteries came out of the same factory production line and got different stickers slapped on them for the different store brands. Brand new batteries on the shelf in the store being bad isn't all that common, so an issue at the factory might explain it.

 

[HenrytheHumvee]

Typically it's the forward battery that overcharges and rear battery undercharges. First in series charges more than later in series. Plus, no two batteries are ever perfectly identical to begin with, so usual recommendation is either install some sort of battery balancer, or swap the battery positions every month or so in order for them to take turns in each position.
Other option is to us 12V chargers on each battery individually every month or so to bring them up to an equal state of charge.

27V while running sounds like an alternator issue that needs corrected. Even with a bad battery, the alternator should be pushing 28V. Anything less won't properly charge up lead acid batteries.

As for the battery failures, it wouldn't surprise me in the slightest if every single one of those batteries came out of the same factory production line and got different stickers slapped on them for the different store brands. Brand new batteries on the shelf in the store being bad isn't all that common, so an issue at the factory might explain it.

Thank you for all the information, I actually just came across another thread on the forum where there is a video showing you how to adjust the volt output on the alternator. I'm going to see if that has any effect.

 

[TOBASH]

I rotate my 24F batteries back and forth every few months.

 

[HenrytheHumvee]

I have an update on my battery saga. I removed the alternator this evening to inspect and clean it. I removed the rear of the alternator and found that one of the resistor leads must have shorted to the case at some point. The resistor is still good and I ended up reattaching it. Hopefully this will fix my issues.

Thank you all for your advice and pointers.

 

[87cr250r]

Remember that your 12v battery is six 2.1 volt cells in series. Rotating pairs of 6 isn't doing much to mix up the 12 cells.

 

[Coug]

Remember that your 12v battery is six 2.1 volt cells in series. Rotating pairs of 6 isn't doing much to mix up the 12 cells.

That may be true, but when 6 cells are receiving less voltage than needed to properly charge and the other 6 are receiving more voltage than needed to properly charge, then rotating the six does help.

It's just the nature of charging batteries in series that the first one connected to positive ends up higher charge than the ones after it, and that not every battery is exactly identical in every electro-chemical aspect.,
In larger battery banks there is either some type of battery balancer, or the entire bank will occasionally receive an "equalizing" charge where all of them get overcharged for a while to try to bring them all back to an equal state of charge. The early HMMWV charging system doesn't have either of those abilities, so the best you can do is either swap them back and forth so they both spend time in the higher charge position, or put an external charger on them and bring them up to equal state of charge that way.

Personally, even though I don't really need it with an A2 variant due to the 14V tap off the regulator to the rear battery, I have a NO.CO Gen5X2 charger hardwired to my batteries, and keep it plugged in when not in use (dash camera is set to record when truck is off, so drains batteries over time) and will charge them both equally/independently.