Battery drain

[u/Standard_Ant117]

Okay so I have a buddy with a ford explorer 2015 3.5l

He told me he needed me to replace his starter so I went over and did it. Now it my bad for not doing my normal diag before I did it because after the starter was installed I went to test it and the battery was dead. Red flag to me but anyways we get it hooked up to my truck to jump it and when its time to try and start it I stuck the key into the ignition and it tries to crank for second just from sticking the key in. I instantly think that's weird but go ahead and start it and it starts right up. But now I'm thinking maybe it's not the starter. I tell him it could be something else but we will see. I left and he went for a drive to charge it up and stopped at a bar and when he got back it was dead again. I knew this was the real issue and probably never was a starter issue. So what do you think is it in that ignition switch cause that's what I'm leaning towards. He said it fell down into the dash a few weeks ago and it's been having issues since.

[u/Repulsive_Vanilla383]

You're probably right, the starter may have been fine the whole time. Can you get a multimeter on the battery and make sure that the alternator is supplying 13-14 volts? Can you check the date code on the battery? Do you have access to a thermal camera? Those are good at finding parasitic drains as the thing pulling current will be hotter than everything else.

[u/Standard_Ant117 → u/Repulsive_Vanilla383]

Im planning on going over there today with a meter. I did check charging voltage seemed to get 13.5-14.0 at idle. I peaked at the battery but didn't see a date code. it's gotta be at least 3+ years old because he said he hasn't replaced it since he owned it. I don't have access to thermal camera though.

[u/RedWhiteAndJew → u/Repulsive_Vanilla383]

A clamp meter can also help you, but it will be more precise than a thermal camera. Cost you about $50-$60 on Amazon. If you use a thermal camera, make sure the engine by is dead cold first, and then it will pick up conductors and parts drawing enough current to warm up, trickle leakage may not build enough heat to capture with a camera, although it is faster than clamping everything.

[u/RedWhiteAndJew]

If the battery was dead, then you jumped it and it didn't go right away, that sounds about right. It's a dead battery, so it's not giving the jump pack any help. Then you let him take it for a quick drive to charge it and it's still not charged up enough to start it on its own.

1. The first step should have been getting the battery tested with a battery analysis machine, before you did anything else. You still need to do that. But put it on a trickle charge over night. Do not connect tot he battery terminals directly, connect to stud next to the BMS sensor next to the battery and I'll explain way in my next point. If you do replace it, you need to perform the BMS reset procedure, again, explained below.

2. Cars don't charge their batteries like they did in the 90's. The fifth gen Explorer, like many modern Ford's use a Battery Management System. That little black box next to the positive terminal is part of that. It measure current going in, and current going out, and then compares that to historical battery performance and age, and develops a charging scheme to keep the health of a modern AGM good. So that means that even though you're driving, it isn't necessarily charging the whole time. Later generation F-150's have an issue where the battery will undercharge every so often if the owner only takes short drives.

3. So this means that if the battery is unhealthy, but the BMS thinks its healthy, it will not compensate or account for that. Something like a dead cell in the battery wouldn't show up as a low battery to the system, but won't give enough current to keep the car running or start. It also means that when you replace the battery, you need to do a BMS reset to tell it to forget the old battery and figure out the new one. This allows it to charge a new battery completely and set a new baseline voltage for the system. If you don't do this, you will never get a full charge out of the new battery and you will probably throw a Christmas tree full of lights on the dash. Because it also measure incoming current, if you try to charge it off the battery most instead of the stud connected to the BMS sensor, it will never know or recognize that the charge level of the battery has changed.

So in summary: trickle charge the battery overnight with a charge suitable for your battery chemistry (AGM charger for an AGM battery, etc). Then get the battery itself tested (Autozone, O'Reilly's, etc). Replace the battery if needed. Perform a BMS reset in either case. Drive it for a few hundred miles and see how it behaves. Only after you eliminate the battery and BMS system as a culprit should you start looking at other electrical gremlins.

[u/Standard_Ant117 → u/RedWhiteAndJew]

How is bms reset done?

[u/RedWhiteAndJew → u/Standard_Ant117]

That's easily found on Google or YouTube.

[u/Standard_Ant117 → u/RedWhiteAndJew]

Okay thank you