Parasitic Draw on battery

Howard H. · Dec 4, 2020

I've got two different vehicles sporadically draining the battery overnight. Most of the time, everything is fine, but occasionally, the battery will be near stone-cold dead after sitting overnight.

Dad had mentioned a few years ago about an faulty alternator on a truck that would do that every now and then (or at least thats how I remember the story ha).

Is that still possible/likely in todays world with 15 year old or newer vehicles? If it only happens sporadically, what is a good way to test for that?

Thanks,
Howard

Dave H (MI) · Dec 4, 2020

I ended up putting a battery cutoff switch on my wife's old Buick she drives for local runs. Very difficult sometimes to figure out where the drain is. I even had a shop look at it. No luck.

old · Dec 4, 2020

Could be a number of things.
Alternator going bad
Door switch that works some time and other time not leaving a light bulb or 2 on
Computer problem.
Or even a bad ignition switch that does not shut off every time

4play · Dec 4, 2020

Alternator is possible, if it's easy to unplug the cables, you might try that. Also look over everything and see if you can see lights on hood, trunk, glove box, vanity lights etc. Most of the time I find draws coming from aftermarket devices. Radio, amps, inverters, brake controllers etc. They might work fine, but pull loads when they should be off. If you have aftermarket stuff, it might be worth unplugging to see.

SDE · Dec 4, 2020

My GFs Saturn Vue would randomly go dead. A few months later the belt tensioner bearing seize up and broke the pulley. After that repair, the battery did not go dead again.

JD Dave · Dec 5, 2020

I find some newer vehicles are more prone to parasitic draw than the old stuff, probably because of all the computers that control and relay everything from the engine management to the interior lights.
A decent test procedure is to remove the fuses and test across the fuse holders with a multimeter set for "amps". The smallest bulb can drain a battery in a couple days.

muleman51 · Dec 5, 2020

I have two trucks that do that. The one truck has a battery disconnect switch and the other we just unbolt the battery cable every night.

Mark Poss · Dec 5, 2020

Had a 90 Chevy Silverado years ago battery would need charging every 3-4 days. Couldn’t find where it was draining. Finally one night I parked it and noticed a glow coming from the glove box. The tab that held the button in for the light switch was broken. Removed the bulb and problem solved

ss55 · Dec 5, 2020

When the radio in my Chevy pickup went bad it would drain the battery while the vehicle was parked. I replaced it with an aftermarket radio.

Determined · Dec 5, 2020

With engine off, key off touch the blade of a screwdriver to the end of the alternator shaft where the pulley is attached, if it grabs the screwdriver firmly you know the alternator is still energized.

Yes this can be an intermittent problem which makes diagnosing very difficult when it only does it once a week.
While not terribly common, seemed I have seen it more on Ford products.

There are countless things that can drain a battery overnight with many being vehicle specific so other than the obvious generic things like glove box or vanity light not shutting off or any recent additions to the vehicle ( stereo, command start etc) more info about the vehicles would be the place to start if you want helpful answers.

Hobo,NC · Dec 5, 2020

My top three for the year.

1) the key could be removed in any position The old gal was not shutting it off all the way. New ignition lock and cylinder was the fix.

2) The brake controller had a more than usual draw. They did not tow anymore its easy to disconnect and connect.

3) The rear wiper would cycle random with the key off, I put a cigarette butt on the wiper it was on the other side the next morning. Removed fuse for rear wiper.

4) several that had a bad battery even a couple with a new bad battery. The fight is on auto parts store does not like to warranty battery's, even the Honda dealer put up a good fight. No one knows how to test a battery all they have is a fancy hand held tester that is useless... It does cut down on warranty cost.

It would help if you told use exactly what you are working on...

I did leave out one I think its the security system I put a new battery in it, it has not been back. Co'V has brought about some unusual ones with folks working at home and not driving every day... I had one this week the dealer told them it had to be driven every day are the battery would go dead... I told them to ask do they crank every car on the lot everyday...

Mike(NEOhio) · Dec 5, 2020

Had a '97 Grand Cherokee that would turn up with a low battery that wouldn't turn over. It was an intermittent problem that could happen three or four times within a few weeks, or go for months OK. Never could figure it out but taking the fuse out of the interior light circuit stopped it.

Howard H. · Dec 5, 2020

Thanks for all the tips and stories!

Ha ha I purposely didn’t say because I didn’t want to get laughed off
the tractor forum.

One is a BMW 330i and the other a Mini Cooper.

I’ve been very cognizant of all the easy stuff and watching for the
slightest clues. Both are electrically stock with no addons. Both
vehicles have known tendencies to do that as they age, but so far
none of the “known weaknesses” for either have panned out.

I’ve been watching for clues like position of blower motor setting
when I kill the vehicle, snooping around at night looking for any light
source like the glove box, etc.

I DID find the electronic heater control valve warm one morning after
a cool night and thought for sure that was the problem on one of
them, but was surprised when replacing that didn’t cure the problem.

That’s why I was asking about the alternator. Thanks, Determined,
for that magnetized field tip!!

I will test each circuit in the fuse panel to try and pinpoint the
drawdown.

David G · Dec 5, 2020

How old are the batteries in each?

MARK ROBKE · Dec 5, 2020

If you suspect the alternator, the next time it is dead, feel it: if it has a draw it will be warm. Mark.

Hobo,NC · Dec 5, 2020

Euro cars are any car with multiple fuse blocks can be a P.I.T.A to isolate the drain (If it has one) I don't allow Euro cars in my shop tho I have been forced to if they were a good customer with a blank check book.. Even then I don't get deep into it...

My advice if you have to take it to a shop take it to one that knows Euro's well...

Hayfarmer · Dec 5, 2020

My girlfriend has a Hunday(sp) Tuscon had problem of battery going dead overnight. Traced it to electric door locks trying to work but couldn't so ran battery down.

Sprint 6 · Dec 5, 2020

Flir brand thermal imaging camera is the best thing I have ever bought for tracking battary drains. Let it sit overnight, then go over the vehicle. Whatever is not ambient temp is the issue. Flir is the best on the market, it can pickup minor temp differences. There are things like an internal short of a bussed electrical center on a Chevy truck I would have never found except for that camera.

David G · Dec 5, 2020

Typically a bad alternator would draw a battery down every time. On a newer vehicle there are so many things I would doubt it is an alternator.

buickanddeere · Dec 5, 2020

Use an ammeter on each fused circuit and find the circuit(s) with the parasite load .
Found a light in the passenger side visor illuminated 24/7 in Mrs B&Ds GMC Jimmy .

David G · Dec 5, 2020

Agreed.

Papaw8 · Dec 5, 2020

I worked on several parasitic drains back when I was an auto mechanic by trade. The strangest one was a late model (at the time) Cadillac. The drain was on the circuit for the trunk release or the closing motor don't remember. I disconnected them and drain was still there. When car was built they had the seat leg partly on the harness to the rear of car. It had barely worn through insulation just enough to pull a slight drain.

zuhnc · Dec 5, 2020

I used to tow my horse trailer with a 2003 E250. Since I moved to MO, the van sits in the barn; might have driven it 100 miles in two years. Battery would run down dead in about 5 days. Found the brake controller was on constantly. Disconnected it, and battery stays up. Bad trunk or hood light switches are a common culprit. zuhnc

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