7.3L IDI Battery Load Test

[Kelster]

Hey guys,
Just wondering if someone can coach me through a correct load test.

I have a Fluke multimeter and with probes attached to drivers side battery it reads 12.5 volts.

With key on and glow plugs heating voltage drops to 10.3 volts.

Cold cranking voltage drops to 6.5 volts, which I think means my batteries are tired and in need of replacement.

Shouldn't matter which battery as they are wited in parallel.

Does any of this sound correct?

Thanks
Kelly

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[Thewespaul]

Your batteries are toast, time to replace them. Make sure you get at least 850cca batteries

 

[compressionignitionrules]

one of your baterries could be toast and you could also have a worn starter, unless you seperate your batteries and load test them you will never know. can buy a cheap "toaster" load tester under $100. corroded terminals can drop your crank voltage pretty damn low too. no sense buying parts you don't need, unless you like that kind of thing.

 

[Kelster]

Hey guys,
Just wondering if someone can coach me through a correct load test.

I have a Fluke multimeter and with probes attached to drivers side battery it reads 12.5 volts.

With key on and glow plugs heating voltage drops to 10.3 volts.

Cold cranking voltage drops to 6.5 volts, which I think means my batteries are tired and in need of replacement.

Shouldn't matter which battery as they are wited in parallel.

Does any of this sound correct?

Thanks
Kelly

Sent from my SM-G930W8 using Tapatalk

Forgot to mention that it's -20C outside and the blockheater is plugged in.

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[DaveBen]

I disagree with compressionignationrules. Aways replace BOTH batteries at the same time. They are tied together so what you have is one battery in two places. You will kill the new battery if you replace just one battery.

 

[Macrobb]

Also want to check charging voltage, make sure it's ok, that your batteries are getting a good charge, and not overcharging.
Overcharging will boil off the water in your battery, resulting in low capacity... and kill a new battery relatively quickly.

 

[chris142]

I disagree with compressionignationrules. Aways replace BOTH batteries at the same time. They are tied together so what you have is one battery in two places. You will kill the new battery if you replace just one battery.

Always replace batteries as a set. If they are not matched yes the old one will shorten the life of the new one. Replacing just 1 will work in a pinch in an emergency. Our trucks will start with just 1 battery unless its extremely cold.

 

[79jasper]

I'm not seeing where he said to just replace the bad one.
I believe he was saying to check the cables and connections also, as no point in buying batteries, if don't need them.
While for most, I'll still recommend replacing batteries in pairs, (as for 99% of people thats easier) it also doesn't make sense to replace a perfectly good battery. (If it passes a load/voltage drop test.)

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[compressionignitionrules]

always replace batteries as customer requests! you will ALWAYS replace both together if you are doing the job right! I've been Truck/coach licenced for just over 25 yrs . have seen lots of cold temps and batteries fail just as much in the summer.
I've replaced 1 battery on my own dual battery vehicle , the one in the box under the body is usually the culprit in a van. if one battery is weak your voltage regulator will not go above its limits when its working properly and you end up not charging your good battery enough. then as soon as you load them down in parallel you basically crank with 2 half dead batteries.

you can also find a weak battery with a charger if you segregate them. put your charger on a high charge 40 amps or so and watch your voltage(multimeter) a soft battery will climb fast and go to 16 volts real quick(60 secondish) , while a good battery will a while to charge and probably creep up to 13 volts if you leave it on for 10 min.

should be lots of no starts around here Wed morning...................................lucky I'm straight afternoons>working foreman

What is extremely cold in SoCal

 

[rgaus]

On dual battery systems...
If one battery is weaker/bad, I replace both batteries and usually test/save the stronger battery for single battery application. Seem to alway have a spare core laying around to exchange.

Bob G.

 

[BeastMaster]

I note mine ( "Interstate" brand batteries... two years old ) drop to 10.5 during cranking... glow plugs still ON.
Electric fuel pump running, but no other loads on the battery.
Outside temp around 70 degrees F.
Starts almost immediately ( 1 revolution or so ) - or around 0.5 second.. usually rwwr-rwwr-rwwr-running.
FWIW, I replaced all the glow plugs when I bought this thing two years ago.

Voltage re-establishes itself to about 14.8 or so within two or three minutes once glow plugs have cycled OFF and the alternator has re-established the charge.

You are running far colder. I have not tried to start this beast in that kind of cold yet.

 

[tradergem]

Compressionignitionrules: When I lived in Mojave, California, the coldest I remember seeing was about 15*F for about a week. I remember that week because my heater core in my 67 Chevy II station wagon split it's seems and I had to drive about 35 miles each way to work with no heat all week until I could get a new core installed.

On average most of southern California gets to between 40-60*F with a few days in the 20-30*F range. However yesterday my son who lives in Wildomar, California said it was 80*F.
That also is not all that unusual for southern California.

 

[nostrokes]

one of your baterries could be toast and you could also have a worn starter, unless you seperate your batteries and load test them you will never know. can buy a cheap "toaster" load tester under $100. corroded terminals can drop your crank voltage pretty damn low too. no sense buying parts you don't need, unless you like that kind of thing.

He never said to replace one battery just to test them separately and check the connections.

Yes you should always change both at the same time, but make sure that is the true issue first. Bad connections will give you low voltage under load.

 

[frankenwrench]

He never said to replace one battery just to test them separately and check the connections.

Yes you should always change both at the same time, but make sure that is the true issue first. Bad connections will give you low voltage under load.

X2. Just had that issue. It wasn't terrible cold maybe 28*f but still dropped my volt meter almost flat durring glow plug cycle. Just needed new connectors and had to replace 3 hot wires. Crossover lead, the small one that goes to relay on fender, and of course the cable that runs to starter. I thought my year old batteries were bad or my year old starter was bad. Just connectors and cables were tarnished and crusty.

 

[RosBaig]

Hi.... That's a speedy and simple test, but take it to less Schwab they'll test your batteries. Meaning they'll put a stack analyzer on them, having 12 volts do not implied squat in the event that you do not have the right wrenching amps. And you having 13 or 14 volts whereas truck running fair implies your charging framework is working. But stack test them, and you'll know for sure. Less Schwab tests batteries without charge I accept, at slightest in my region they do.