So I parked my truck in the driveway Wednesday afternoon after my normal day of driving. Saturday Morning I went out to move it back because I was rearranging the garage. I hit the unlock button and nothing. I unlocked it with the key and put the key in the ignition and absolutely nothing happened. Not even a door chime or an interior light. So the batteries were dead. I can not figure out what killed the batteries. All I had plugged in was 3 usb chargers. 2 of them had nothing connected and the third has just my little cell phone I use for Torque. I find it hard to believe that would drain 2 750amp batteries in 2 days, plus it never has before. So, I hooked it up to the van but it wouldn't jump it off. I was getting 14v to both batteries through the jumper cables but it didn't start. My battery charger is only a little 6amp Sears charger. I hooked it up and let it charge while I was working in the garage. A few hours later the needle had not moved but I unhooked the charger and had 12.1 volts so I hooked the van back up and jumped it off. I drove it about 40 miles at 65mph and Torquepro was showing about 14.5 volts at highway speed. I parked it and it would start on its own. I waited a while and checked the batteries again and it read 12.41. I hooked up the charger and charged it a few more hours. Sunday morning I checked it and still 12.4v. I hooked up the charger and charged it more. The needle moved down to about 5amps for a while but when I unhooked it in the afternoon it had pulled down to about 2.5 so I know the batteries were charging. I drove it quite a bit yesterday and it seems fine. I don't know what happened. Nothing was left on. The headlights are set to auto and the doors were all locked shut. The only thing out of normal was that sirius was displaying "updating sirius 0%" the whole time during the first drive. That went away when I restarted the truck. So I guess some kind of crazy computer glitch was running something for two days and killed the batts??? If anybody can think of anything I should check I would like to hear it because I am baffled on this one. If it starts ok today, the only thing left to do is isolate the batts and see if one is bad I guess.

 

If you want to be on the safe side. have the batterys load tested separately. One battery could have a weak cell.

 

That is what I am thinking. I will have them tested asap. Will they be covered under warranty? They have been in service fro 24mos and 18k.

 

Happened to my '14 SD.....found bad cell in one battery. Be sure to replace both if one is bad. They depend on each other.
Good luck!

 

Make sure you disconnect one battery lead when getting them tested. The are connected in parallel, and when connected act like one big battery and will mask a bad cell when getting them load tested. I argued with the clerk at autozone this fall, and in the end caved in since he was the "expert". A day later my truck wouldnt start. Went back, and insisted that we disconnect one of the batteries and retest, and low-and-behold, passenger side battery was reading bad.

He told me that his procedures required him to remove the battery and put it on the charger for a couple hours. Thats when I replied with, "do you expect me to shop your store for 2 hours?" His reply was "no, you have a second battery in your truck, just come back...."

Thats when I knew I had to explain to him that the truck required 2 to run. Told him if he is refusing to replace the battery under warranty, to just sell me one. He replaced it on the spot.

 

My F150 battery died in its 2nd winter on a day similar to this. It started at home, at work all day that never went above zero, and nothing when time to go home. Only a jump start got me going. Replaced the 770CCA Motorcraft with a Kirkland 850CCA and never had any trouble after.
FWIW, if those chargers had the adapter (12v plug) on them, they still draw power whether plugged into a device or not. I have a dual output 12v/USB adapter that has a green light when it is on, so I pull it part way out when not in use. My CTS gauge shuts down automatically and my Magellan GPS shuts down when it detects no movement after x amount of time.

 

I thought mine were dead and it was the starter...water got in the temps dropped big time and it froze..even thou the wife took it too work 2 days after the rain. Go figure..after short order and warm ups the starter worked fine for over a year before I traded. I didn't get any juice at the battery..odd... thought for sure the batteries were dead.

 

I haven't had time to test them yet. I went through this same deal with my 6.0 a couple of times. One of my batts went bad and I replaced both. The next year one of the new ones failed and I replaced it. It just sucks dealing with it already. All I had time to do today was check the voltage on it while it was cold. 12.51 with both connected. That is only about 80% so there is a problem somewhere.

 

The voltmeter check will tell you have a problem, but not isolate a bad cell(s). A battery at 12.5 volts may or may not have enough reserve power left to turn over our big starters. At least that's my experience the past two times, once on my '13 Ford Edge.
Have it load tested is the only way.

 

you probably know one bad cell will drag both down..

 

Is it true that both batteries are required to start the truck? Is it a matter of the circuit is disconnected when one battery is removed, or does the truck physically need that many amps to start?

 

well, my truck wouldnt start with one bad battery. it would try, but wouldnt complete the cycle, i.e. it would crank slow, then quit. it was cold out, cold engine. *maybe* if warm out, and engine warm where glow plugs may not have played a big part of the load, might be a different story.

 

Mine is still starting and charging fine. I haven't had time to have them load tested but I assume there is a problem with one of them. As far as starting on one battery goes, if one of mine was completely dead then the one I used to jump start it made up the difference. I guess you could simply unhook one of them and see what happens. I think the high compression may be the reason two batteries are necessary.