An electrical issue

[Kenworth guy]

Hello everyone I’m new here, I have a problem on my 2017 Kenworth T680 Batteries dies really fast I checked the alternator and measured 14.4 v
Going to check battery pack, and each battery separately, volt gauge used to show me 14.2 v now shows 13v as soon as I turn my lights on goes down to 12.8

 

[Will L.]

You need to separate all the batteries, then do a load test on each one.
I have been using this harbor freight tester for like 25 years- don’t bother with a more expensive one. https://www.harborfreight.com/100a-612v-battery-load-tester-61747.html
If one battery is low or bad, it will drain and kill the other(s).
Clean all the connections while apart.

If that is good, next thing to do is ‘parasitic draw’ test. Reconnect the batteries- connect all the positives, connect the short cables to the negatives. DO NOT connect the last negative cable from the truck to the batteries yet. Put an multi meter- digital amp meter set on highest amperage setting. Put it inline so the positive tester lead is to the negative battery post, and the negative tester lead to the negative cable. Read the amperage draw and write in down. Pay attention to note amps or milli amps.

I don’t know the acceptable amperage draw for your truck. But if it is over 50 mA (milli amps) I would think you have too large a draw.
watching meter and removing then reinstalling one fuse at a time is how most are found.

 

[MrMarty51]

I have used an elcheapo battery tester just like the one Will L shows. They are good units. I dont remember for how long to hold the load test switch but the instructions should say.
If You find one bad battery, do not mess around with changing just that one. Replace them all in sets.
The other batteries most always are not to far from a failure and they will destroy the one new battery in a very short while.

 

[dbrannon79]

Do like Will says and load test batteries first, then the parasitic draw test. when load testing the batteries, do them separately and don't trust those electronic digital style load testers. they don't put a real load on the battery cells. if everything passes, I would connect an amp clamp to the positive post on the alternator and make sure the alternator isn't dieing. at my work we service several kenworth t800's and t880's we have a PM program to replace the starters and alternators before the trucks get to 400k miles. the alternators usually begin to fail by the internal diodes giving out. once this happens the alternator will output good voltage with everything off and the truck idling. once a load is introduced like headlights and ac the voltage starts dropping. this PM program has saved us from having to make road calls to replace them out in the middle of nowhere!

a word of caution.... if you smell something from the battery compartment like rotten eggs, get a face shield on and cover your self with a water proof barrier like a thick rubber rain suit. if one of those bateries pop, it's game over with a trip to the hospital having acid burns. I know the rain suit isn't going to protect you but for maybe a few seconds, but it's long enough to get it off and have a buddy near by with a water hose to rinse you down saving your life.

 

[MrMarty51]

And never smoke or have any kind of a flammable substance burning near a charging or discharging battery. One of the ingredients emanating from the battery smell is hydrogen.
Remember the Hindenburg, big old fire, except for instead of a fire, it will be an explosion, battery caps flying, might even bee shrapnel from busted battery case.

 

[Rockabillyrat]

You need to perform a batter draw test.

Disconnect the negative battery cable and put a amp meter on it. One end on the battery and the other on the negative cable. Then let it sit for 30-45min and see what draw you have. The maximum spec is about 50-60 milliamps. Anything more would cause the batteries to drain.

Its a good idea to close the door adjar switch but leave the door open so you can access the fuse box. Alot of times you can just push the latch in to fool the BCM that the door is shut. If you have too much of a draw then voltage drop each fuse to find the circuit causing the draw. Put your voltage meter in millivolts and put each lead on either side of the fuse. If you see any voltage dropping across the fuse then that circuit is currently active. Thats the best way to find a draw, you should avoid pulling fuses one and a time on modern trucks because of all the computers.

 

[dbrannon79]

I never thought about doing the test that way @Rockabillyrat, makes good sense though. Suppose I would be dangerous around rigs with modern electronics! haha..

I have always used a test light between the battery post and the cable when disconnected, then with the door open and the adjar switch closed, start pulling fuses one by one till the test light goes out or really dim. I have found that most of the time it's ether four of things... the radio, brake light switch, failing vehicle alarm or a stuck regulator in the alternator causing the issues.

 

[Rockabillyrat]

Pulling fuse still works, especially on older vehicles. But with modern trucks having 45+ computers in them it best to only pull a fuse after you confirm its the source of the draw with a voltage drop test. It can take up to a hour for a computer to go back to sleep if you remove and reinstall the fuse that powers it. Kinda hard to be efficient finding draw when you have to keep waiting. Also some computers require recalibration if they lose power so you might be forced to take it to a mechanic just because you removed the fuse.

 

[MrMarty51]

And here I was going to suggest removing the fuse to the ECM so that would not be producing a voltage draw.
Guess on some newer rigs that might not be such a good plan.
Be real bad if the battery all a sudden died. Have to get the ECM recalibrated then too.

 

[Will L.]

Pulling fuse still works, especially on older vehicles. But with modern trucks having 45+ computers in them it best to only pull a fuse after you confirm its the source of the draw with a voltage drop test. It can take up to a hour for a computer to go back to sleep if you remove and reinstall the fuse that powers it. Kinda hard to be efficient finding draw when you have to keep waiting. Also some computers require recalibration if they lose power so you might be forced to take it to a mechanic just because you removed the fuse.

So recalibrate every 3 year when batteries get changed? Holy smokes.
They sure went stupid since I quit wrenching on them.

 

[Rockabillyrat]

So recalibrate every 3 year when batteries get changed? Holy smokes.
They sure went stupid since I quit wrenching on them.

Basically, things like adaptive cruise, electric power steering, and yaw rate will all need recalibrated if batter power is lost. I had a BMW the other week that took me 30min with a scanner to get everything working again after I had the battery disconnected.