24V system batteries sucking

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amaurer

amaurer

Joined
Sep 2, 2007
Threads
373
Messages
4,438
Location
Longmont, CO
My BJ73 has a two-battery system (two 12V in series).

For the last 6 months I've been having a problem where, without warning, the truck won't start.

I'll disconnect the batteries and measure the voltage and find one to be very dead. I charge it up, put them both back in and everything is good for another month.

Either battery appears to be able to fall victim.

When both batteries are reasonably charged (or just not super dead) I get good voltage from the alternator. When one of the batteries goes super flat, however, the alternator can't bring it back to life - it needs to be removed and charged manually.

Batteries are 5 years old.

I have NOTHING attached to just one battery or the other - I know that causes problems.

What do you think?
 
anything going on with your headlights?

I had something happen once where one stuck on and killed a battery...

Course the bright light is a bit of a tip off there...:lol:
 
seapotato said:
anything going on with your headlights?

I had something happen once where one stuck on and killed a battery...

Course the bright light is a bit of a tip off there...:lol:
Click to expand...

Nope, lights are good. Also I have 24V headlamps so I don't think the "one on each battery" shenanigans applies to my truck.
 
Don't waste your time Drew.

When a battery goes flat and it's five years old - just dump it. (And in your case "dump both" because we know 24V system batteries are always replaced in pairs ... and with batteries of identical brand and batch.)

At 5 years old a battery is "past its use-by date" so to speak.

And of course never skimp on the quality of the batteries you buy.

There's nothing so annoying as having your vehicle let you down by failing start when you're camped in freezing conditions in the middle of nowhere with no-one else for miles around (..... assuming you can find such a place in California :lol:).

I actually automatically dump my battery now as soon as it reaches 5 years old even though it is usually still cranking my engine as good as if it were new.

So if I was you, I would only start investigating for faults if the "new matched-pair quality batteries you fit now" start letting you down as well.

:cheers:

(In other words, I think both batteries are "highly suspect" just because they are 5 years old.)
 
Yes, Lostmarbles is spot on . I had a set that was under a year old but one battery seemed to be bad. Then your system cooks the other battery because it does not charge batteries separately. Even if you charge them up seperately on a charger, they will still be a bit different in how they charge and hold a charge. You best bet is to give them to someone with a 12V vehicle and get a new set. Since reading Greg_b's post on this issue, I have always asked for two batteries of sequential serial numbers to ensure they are as similar as can be.
 
It is November. I've heard californians don't like the cold so maybe neither do their vehicle. I recommend a battery blanket (two of course because it's a 24V), a block heater, an inline coolant heater, oil pan heater, and maybe a ceramic heater to sit inside the cab so the plastic doesn't crack.

IF your vehicle doesn't start then, maybe try new batteries.
 
Hi Drew,
What you can do is buying a tester to figure out how bad each one is with a tester.
They are $25 or so. Saves you a lot of time on charging, testing, charging and so on.
AccuTester_055131.webp

Rudi
AccuTester_055131.webp
 
bj40green said:
Hi Drew,
What you can do is buying a tester to figure out how bad each one is with a tester.
They are $25 or so. Saves you a lot of time on charging, testing, charging and so on.
View attachment 573045

Rudi
Click to expand...

Here's my version Rudi:

BatteryTest.webp

And we all know "Older is Better"!!!!!!!!!!!!!!!!!!

:beer:
BatteryTest.webp
 
Although the age of your batteries is probably most of the problem if something in your electrical system hasn't changed in a while...

It's easy to test for a parasitic drain with any cheap multi meter you just need to put the meter on DC mA. Start on the highest setting on the meter disconnect one battery cable anywhere in the system and put the meter in series between the disconnected cable and the battery post it just came from... Whatever mA reading you get is how much your deck/clock/equalizer etc is draining from your batteries to keep time or do it's job....

At least to me there is no point in buying a battery tester when any place that sells batteries weather it's a car parts store, interstate or even Walmart should test your batteries for free and usually even charge them for free and let you the condition...

With any 24V system batteries usually don't last there usual lifetime, especially with 12v taps. So when purchasing new ones make sure you keep all warrenty papers and look for batteries that offer a really decent free replacement period... Although I don't love eliminator batteries (exide make) Canadian tire handed over two new batteries to me worth over 250 bucks almost 3 years after the original purchase! No questions asked...
 
I do have some constant draw - my voltage converter is always "on" keeping my radio presets alive. It has a cooling fan and some "dark" current of its own. I had assumed this wouldn't kill batteries as its not center tapped - it runs off both of them. Are we saying that any constant draw at all will eventually kill a 2 battery system?

I can modify it so the converter shuts off... but I'd have to open the dash again.
 
I had a similar problem until last month. I had one battery that would go to 10.5 volts all the time (amazingly, the truck was still starting) My suspicion is that the battery was damaged in a period in which a headlight had burned out and I didn't notice because it was the summer and I wasn't driving at night for several days. After the headlight was replaced the battery kept having problems until I replaced the pair. No worries since.
As an aside, I find a good long replacement warrantee to be a good investment for these 24 volt trucks (6 year free replacement for the ones I have now)


Anyway, you said that you have nothing tapping off one battery - maybe make sure there is nothing shorting a post of your battery on the hood or anything else that could be tapping power from one battery. If nothing there, maybe one cell of your battery has gone bad and is causing an imbalance.


Some 24 to 12 converters have a significant draw if left on all the time. I had to put a switch on mine and run a small 12v gel cell for the radio memory. I also put a battery kill switch on the main battery cable for leaving the truck for extended periods of time.
 
yes it will eventually kill both batteries just not as fast as a center tap. mine goes dead in 2 weeks if I let it sit. Although I think I have one bad battery. Putting the converter on a switch is a good idea that way you can leave it on if you know you are going to be driving it lots or turn it off if you know it will be sitting for a while.

I purchased two identical chargers that will float when they reach full charge. I don't have them permanetly mounted but will soon. Come home, plug it in and I know it will always start.

Other than the nice fast starting I'm not a fan of the 24v system. Maybe if you could get one big 24v battery!
 
Yes any draw on even perfect new batteries over enough time will bring both batteries down enough that it will cause a no start condition... Although with new batteries this could take several weeks...

On my setup which is going from what Stone originally posted, sorry I can't find the link to that thread... I do however have my diagram of the setup which I posted below...

I can switch from manual load balance to strict convert mode. However over time the unit will run the batteries down enough to cause a no start situation. I just purchased a shock and water proof 5A battery tender that will go on the 12V battery and after the truck sits a while I can just plug it in for a few hours (or overnight) and have two perfectly equalized topped up batteries...

Although it requires a 120V outlet, I think it finishes the system off nicely... They don't recommend disconnecting and reconnecting the leads all the time either, I've been told by the company it can damage the unit. I just thought this was a simple permanent solution and any time the truck is going to sit for a week or longer there will be an outlet fairly close by.
Battery setup.webp
 
I will just move the converter to the switched part of the truck harness. A 12V zener diode on the radio memory terminal will be plenty to keep it alive.

I still don't grasp why a small constant load will cause one battery to drain... but I suppose thats just an old battery phenomenon.
 
jensen makes a heavy duty radio that has a built in memory battery. Its built for truckers and machines so it should be pretty tough.
 
amaurer said:
I still don't grasp why a small constant load will cause one battery to drain... but I suppose thats just an old battery phenomenon.
Click to expand...

It's the "old age" phenomena. The chemical recycling process stops at a certain point. One battery sooner then the other.
It's the same as multiple batteries in a flash light. One day the light starts dimming. You replace ALL batteries and you are OK. Now measure the old batteries and you'll find different voltages for each battery but the one with the lowest voltage (= highest internal resistance) is setting the maximum output for the bulb.
What hurts is that a set of flashlight batteries is cheap but a pair of car battery is expensive. You can manipulate the acid value and other little tricks like the charge current, but the final line is that the battery is dying. End of story.
Sorry for the sad news.

Rudi
 
bj40green said:
You can manipulate the acid value and other little tricks like the charge current, but the final line is that the battery is dying. End of story.
Sorry for the sad news.

Rudi
Click to expand...

My batteries are apparently fighting for the title of "the one thats dying" but point taken. No biggie, replacing them isn't a big deal.

Thx.
 
Didn't you have electrical issues on your journey from Chicago to Cali? What happened then?
 
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