Hi,

I have a 2008 F250 6.4 with 350000km.

My batteries were both replaced a week ago. I had poor CCA at 6.2 and on warm days hard to start, 9 years on those.

My truck has sat for 5 days I turn it on and my truck dies after 5 minutes. My primary (driver side) battery is dead. I charge it and reinstall, truck is on no problem at this point. I tested my passenger battery while truck is at idle it reads 14.2, driver battery reads 12.3. I have a single alternator.

Alternator going bad or is this regular values?
I have to mention I had wayyyy too much dielectric grease on the battery that died it has been cleaned now.

Thank you for reading my post.


*** did a 20 min drive values remain the same and after truck is turned off batteries read 12.5 and 12.2

 

Are you testing batteries separately? They must be disconnected to test. One battery can be shorted internally and pull the other battery down. If you are getting 14 volts while truck is running, alt is good.

 

Sounds like the first thing to be done is get the batteries charged and equalized. The alternator can't do this, unless a road trip to Montana and back is in the cards.

 

Thanks for replying.
I am testing them separately disconnected getting 12.2-12.7 which are correct values. When I test them connected while truck is on I get one correct value at 14.2 charging and the other is lower...find it odd how one is charging at the right value but not the other or is this normal for a diesel?

 

haha that's a far boot from Ontario but I did have them both on the charger over night.

 

Keep in mind there is only one battery electrically speaking. Both "halves" need to be on the same sheet of music in terms of internal cell resistance and charge. Modern sealed maintenance free batteries are fully charged when they read 12.80 volts at rest, at 77° F. The "surface charge" has to be removed before measuring this.

If one battery "half" is at ~ 12.0 volts and the other is at ~ 12.5 volts, one is almost dead at at 25% charge and the other is maybe 50% charge. It takes a big *** charger to equalize them in a reasonable safe time frame when connected together. Or charge them separately with a regular automotive charger of 5 to 10 amps. Both batteries need to read 12.80 volts at rest. New batteries are "hard" and won't reach their full rated capacity till they get a little use for a while. A tenth or two of a volt doesn't like much but it is a huge percentage with a battery. The difference between "100%" and "Dead" is less than a volt.

 

Thanks a lot for the comprehensive reply. I drove one hour on those new batteries then 5 days later started my truck and a few minutes later died.

Why would a new battery die like that? Again I had an excess amount of grease on the terminals.

So you recommend I charge both separately and check the 12v value? Do you believe the reason I am receiving odd values during the alternator test is because one is compensating the other?

Electrical has always been a weak point for me.

Thanks

***driver battery is 11.8v, after charging it yesterday. Have it on the charger again and is reading low so its clearly not being charged by the alt.

 

It takes a long time to charge a battery with a typical automotive charger. The charger, in terms of amperes, needs to be "sized" roughly speaking to the battery in question. A battery will accept (or draw) just as many amps as you throw at it. What size charger are you using? With a typical Schumacher or classic charger this might take a couple days to get them both plussed up. Letting them cook for a while at around 14.5 volts. If you can measure the end state current or specific gravity that will tell the tale.

A 50 amp charger will bring even a dead battery to 90% very, very quickly. Maybe a half hour or so will get you on the road. Not fully charged, but enough charge to crank the engine. But it creates a lot of heat internally, and a fast charge may cause damage or buckling to the plates.

On the other hand, a 12 volt wall wart with little more than 0.1 amp current will also recharge a battery, but it will take a week and a half and it will be boiling the electrolyte away the whole time. About 8 to 10 amps is the typical size charger for a single automotive starting battery. Fast enough for a reasonable time frame, slow enough for a thorough complete and deep charge. But it won't be quite enough for two batteries connected in parallel.

Or put another way, it will take just as long because two batteries connected in parallel have the same voltage, though twice the ampere hour capacity. But the idea is to avoid one battery half from hogging all the current while the other half is outgassing heavily. Outgassing is good, but it needs to be minimized. This is what happens when you're driving around with undercharged batts. Both halves should be roughly matched, this is why they are replaced in pairs. Or both halves more correctly.

They have the same internal resistance, and age. Once the cells become mismatched, one battery has permanently sulfated plates due to a chronic undercharging, they will never be "matched" again and one battery will always hog more charge current I'd expect.

 

I don't understand why you would use dielectric grease on battery terminals, after all its as an electrical insulator not a conductor. You need to verify your cables for corrosion, if you have had issues with corrosion it soaks up into the cable and renders them useless.

 

Well that's the next thing, when he gets the battery charged he can test the alternator and cables .

 

How's it going, any luck?

 

If he has 14.2V at one battery with the engine running then the alternator is working as designed. The issue is either the other battery or the cables and terminals.

 

Well you're right, I should have said charging system, grounds etc, the whole shootin' match.