Battery drain issue which terminal to disconnect?

Thread starter #1
Mini van keeps draining its battery and killing them. I just recharged the current battery and want to disconnect it to keep it from running down; positive side or negative side or both? Its a back up vehicle that we don't need to drive very often so I'm in no hurry to pay someone to find the short or drain. Any advice is appreciated as always.
 
#4
isn't the correct answer either? It has to be a closed loop for current to flow.
You should always disconnect the negative cable first. If you disconnect the positive first, there's a chance of touching the wrench to a metal surface and causing a spark but you're right about the closed loop.
 

Milkman

Retired Moderator
#5
Mini van keeps draining its battery and killing them. I just recharged the current battery and want to disconnect it to keep it from running down; positive side or negative side or both? Its a back up vehicle that we don't need to drive very often so I'm in no hurry to pay someone to find the short or drain. Any advice is appreciated as always.
I have disconnected my tractor like this for over 25 years. I put a battery post with a stud terminal and use a wingnut to attach the cable. I do the negative wire.
 
#7
Run a tractor that way for years. always the neg.

There's a reason, but I forget what it is.

Sort of funny story (like if it didn't happen to you funny). We have a Ford tractor. It wouldn't start, appeared to be a dead battery, We did all the usual things charge the battery, clean the terminals - nothing, not a click.

We bring a mechanic out to the middle of our deer lease (it's a natural law - the tractor always breaks down as far away from the gate as possible. ) He goes over it -nothing, not a click. So we start at the starter switch, which is on the hot side of the battery, disconnect and clean every terminal, no continuity - it's dead.

We get to the starter and head back to the battery on the neg/ground side which is straight shot. Right below the battery but underneath the hood where you couldn't see it was this doohickey about the size if a snuff can. Which had battery cable on either side and nothing else.

It was smoking hot on the battery side, and dead as could be on the starter side.

It didn't look like anything we had seen before. Finally we figured out that it was some sort of battery cut off switch, but it required a special key, which we didn't have and didn't have a clue as to what it looked like. We jacked around with it an hour or so - we could have removed it and straight wired it but we were concerned that it was fused. Finally us geniuses figured out that we could take the tips of some needle nose pliers as a "key" and turn it with a pair of slip joint pliers.

We turned it, the tractor cranked up, and away we went. We figured that over 30 years the switch had vibrated to the off position, it was factory but we couldn't find a reference to it anywhere. Don't know but that it may have been an option.

Never happened again.
 
#8
I was going to suggest a battery cable switch. Don't know where you are at, but I got a new one up yonder in the shop you can have if you are close.

Ooopps....i see now you are in South Ga !
 
#10
you might consider buying one of those 9v memory retainers that you plug into the lighter to keep the computers from losing all the radio presets, transmission shift points, etc when you disconnect the battery. They are used all the time in shops when the battery has to come out.
 
#11
Mini van keeps draining its battery and killing them. I just recharged the current battery and want to disconnect it to keep it from running down; positive side or negative side or both? Its a back up vehicle that we don't need to drive very often so I'm in no hurry to pay someone to find the short or drain. Any advice is appreciated as always.
Might see if you have a under the hood light staying on.

Since it is draining the battery then it is sparking pretty good when you touch the *** batt cable to the battery.? Pull a row or a couple of fuses and touch the cable to batt. If it still sparks replace those fuses and try a few more fuses until it stops sparking. Then narrow those few down until you find which fuse it is. That will tell you what has a draw on it. Gives you a direction on where to look for your problem to correct it. If you do this and track the draw to a fuse, post up what it is and we can chime in on how/where ti fix it.
(alarms and cab/door lights/hood lights in my past have been issues)

Oh, Neg if just disconnecting the battery

edit: Make sure it's not the battery/alt itself causing the problem
 
Thread starter #12
Might see if you have a under the hood light staying on.

Since it is draining the battery then it is sparking pretty good when you touch the *** batt cable to the battery.? Pull a row or a couple of fuses and touch the cable to batt. If it still sparks replace those fuses and try a few more fuses until it stops sparking. Then narrow those few down until you find which fuse it is. That will tell you what has a draw on it. Gives you a direction on where to look for your problem to correct it. If you do this and track the draw to a fuse, post up what it is and we can chime in on how/where ti fix it.
(alarms and cab/door lights/hood lights in my past have been issues)

Oh, Neg if just disconnecting the battery

edit: Make sure it's not the battery/alt itself causing the problem
I disconnected both and 2 days later reconnected and it started up fine. You are right it does spark when I connect or disconnect and its either terminal that does that. The battery is brand new and the alt was tested and was putting out around 14 volts.
 
#13
I disconnected both and 2 days later reconnected and it started up fine. You are right it does spark when I connect or disconnect and its either terminal that does that. The battery is brand new and the alt was tested and was putting out around 14 volts.
if you disconnect it and then connect it back, it will spark. The computer draws power all the time. The way to properly test is to use an amp gauge to test across the fuses for amp draw. You know you will have amp draw feeding the PCM, BCM, and radio constantly. So, it will be a matter of checking each fuse and seeing where the power is going.
 
#14
If it is draining over night the the spark will be a pretty good spark as stated above. Cpu and memory spark is small and barely noticable spark. You will know the difference when you find a overnight/battery dead draw over a memory draw.
What year,make, model is the van? Does the van have any aftermarket stuff add such as a stereo system, alarm, extra lights, trailer plug ect...? If it does, that is where i would start. If you are not meter friendly then the fuse pulling method should find where your issue is and anyone can do it without any tools. I would guess it might take 15min to find where the draw is.
 
#15
Mini van keeps draining its battery and killing them. I just recharged the current battery and want to disconnect it to keep it from running down; positive side or negative side or both? Its a back up vehicle that we don't need to drive very often so I'm in no hurry to pay someone to find the short or drain. Any advice is appreciated as always.
Check your ABS module. They will burn out without lighting dash sensor. They will keep power pull going even after ignition is off.
 
#16
Another thought, try unhooking the wires on the alternator for a few days and see if it will start. If so either replace alt. or get it repaired. Its a very common problem that I've ran into. So much so that it was the 1st thing I would check in my shop.

You state alt was tested, was it fully tested by a repair shop or just checked to see if it's charging? It can charge and still do what I'm talking about.
 
#17
Another thought, try unhooking the wires on the alternator for a few days and see if it will start. If so either replace alt. or get it repaired. Its a very common problem that I've ran into. So much so that it was the 1st thing I would check in my shop.

You state alt was tested, was it fully tested by a repair shop or just checked to see if it's charging? It can charge and still do what I'm talking about.
yep, leaking diodes will kill a battery every time
 
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