Hey guys, I'm chasing a weird problem. Yesterday I went to start my truck and for the first time ever, the batteries were too weak to start it. My brother jumped it and it was ok for a few hours. Here's how the afternoon went.

1230pm, jumped truck, ran for 30 minutes, parked and shut off
215pm, truck started fine, drove for 5 minutes and parked
4pm, truck started fine and I shut it right off
6pm, started fine again! drove to BK for lunch about 10 minutes running
11pm, no start, volts down to 11.7 with key off, hooked up 10amp charger
1245am, came back to try starting it, volts had gone down! jumped it again

After all this, we got it back to my garage and checked the amp draw, it was around 700ma, FSM says it should be under 100ma. Started pulling fuses and #15, 5amp for the GEM and a few other things dropped it below 100ma. I left the fuse out overnight and the truck fired up fine the next morning. Voltage with the key off was 12.5. I drove a few places today and had no issues. Each time I pulled the fuse out when I parked. Came out at 11 tonight after work and the volts dropped back to 11.5. Obviously something else is up. I'm starting to wonder if one of the batteries went bad, managed to hold a charge overnight, then died again today. Is that possible? Sorry for the long story. Any ideas??

 

How old are you batteries Trevor? if more than 3 years old go to Wally World and change them out for some 1000 CA ones. That is what I did. If less than 3 I would put a load test on each one of them to see what that reads.

 

After making sure they are fully charged...

 

check your connections at the alt also. I know it seems stupid to say but I have been chasing a charging problem with mine for the last 6 months. turns out the Batt feed wire was broken almost in two, thus allowing very little current back to the batts. found this the other day when I when I was trying to figure out why the blasted thing wasn't charging AGAIN!. I was checking the plug connector to make sure it was tight and when I wiggled the Batt wire it just came off in my hand. broke right at the crimp. wire was all black and nasty looking. has to have been going on for a long time.

Barney

 

They're both 39 month old 850cca Motorcrafts from Ford. I'm convinced there's a dead cell in both batteries now. The drivers side one will only hold 10.8 volts and won't take a charge at all anymore. I left it disconnected and was running on only the drivers side. It worked for 2 days but now that one's dead too. It also drops to 11 volts with the truck off so I doubt I'll be able to put them on the load tester. I had it on the charger all day at work too. The truck will start up and run if I use the jump pack. The alt puts out a good 14 volts constantly and everything is clean and tight as far as connectors go, so on Monday I'm heading to the dealer to get some new ones. Probably going back to the 750cca's since they originally lasted 7 years.

 

Get a battery hydrometer from napa.. about $20 and you can check each cell for condition.. (make sure the batteries are up to full charge before you check them )

 

You may have had one battery with an internal short that was draining your other remaining 'good' battery. And then the heavy draw from the 'good' battery to the shorted one took the good one out also. I went through something similar last fall, but was able to figure out that one was shorted before damaging my other good one. And my batteries were only 6 months old. I observed excessive arcing when connecting the positive cable (the one that connects the two batteries in parallel) to the second battery - after the other end had already been connected to the other battery.

 

Wished I could help Trevor, only to say what Jim said, load test. Do those Motorcrafts have the water level test caps or are they sealed ?? cant remember..

 

If either battery reads in the 10 volt range when measured separately indicates a shorted cell in that battery. Time to replace (both) batteries. Do not load test a battery with a shorted cell, that's when they blow up!!!!!!!!!
Nick

 

Thanks for the heads up. Never heard that before Nick, still learning..

 

big poppa,
No problem, retired from a telcom company that used a tremendous number of wetcell batteries. A normal lead acid/antimony battery will produce about 2.05vdc per cell. since our batteries are a 6 cell battery, that equates to 12.30vdc. Your reading of 10.5vdc meant that one cell had a short.
Make sense?
Nick

 

I was having the same issue as the op in February with my Motorcraft batteries. I took my truck in to have them tested 3 days before the 3 year warranty was up and both batteries ended up being bad. Ford replaced both of them with no problems.

 

I noticed that arcing too. Now the huge amp reading that showed up when I tested the draw makes sense. I forgot to pull the positive off the other battery and it was pulling 43 amps from one batt to the other!

They have the test caps, and all the cells are full. I didn't even bother testing the electrolyte since it refused to take a charge. First thing I thought when that happened was a dead cell.

Oops! I did try load testing them. Guess I lucked out this time. Now I know better then to try that if it happens again.


We'll see how it goes tomorrow. Mine are 3 months outside of the free replacement. I'm gonna try to get them to give me a set of the 750's for free. My brother and I were talking about the plates in the battery and how they'd have to be thinner in the 850's compared to the 750's to fit in the same case. He thinks that's why it failed earlier then my original 750's, which lasted around 7 years. Does that seem right?

 

Yep, I got it..

 

For future reference, I doubt you're recharging the power lost during cranking by driving for only 15 minutes. A battery that stays below 80% capacity will sulfate quicker, and die sooner, than one that's fully charged at least occasionally.

Lead-acids will charge up to 80-85% quickly but need hours to get that last 15-20% charge.

I didn't see where you'd put them on a charger to make sure they were ever at full capacity.