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Battery Keeps Dying

I have a 1990 Nissan Pickup/D-21 that my dad gave to me when I went off to college. After a while the battery would die for no reason. I’ve done quite a few thing to try and prevent it from happening. So, I finally went to get it looked at. The guys at the shop said it was just a bad battery and so I replaced it. It’s been working fine until this weekend. I went out to my truck today and the battery was dead. The only thing I have noticed about this problem is that when ever it gets cold, the battery seems to drain. It first happened and the beginning of winter when it first started getting cold and now it happens again when it get cold. Any suggestions?

Here is the best I have seen, as I copied it and present it.
Does your Fluke have an ammeter?

Make sure all lights and accessories are off.
Put the ammeter in series with the battery.
Give it a few minutes for whatever electronics to go “asleep”.
The current should drop below ~0.2 amp, preferably under 0.1 amp (100mA)
If not pull fuses one by one until the current drops to normal.

I recently did this for my neighbor and her recently purchased BMW.
The current was ~100mA except for a short 7 amp pulse every 10 seconds or so.
Turned out to be one of the electric seats.

Circuit smith is right. The actual spec on that car is 35 milliamps draw (.035 amps). A litrtle easier and faster way yto find your draw would be to set the ammeter up as described before. Instead of pulling fuses try and get your hands on a second voltmeter. set it to millivolts. measure across the fuses, and unless you get a reading of 0.000mv there is voltage being eaten on that circuit. Also it helps to break the electrical system into sections.

Before you start going all McGruber on your 20 year old car,

When did you install the most recent battery? If it worked fine until this weekend, are you saying your new battery is behaving like your previous battery?

If this only happenes in cold weather, do you have some ice forming somewhere that is causing a short? Just a thought.

My '91 started doing the same thing a couple of years ago, particularly in cold or damp weather.

Turned out that the battery’s negative post was touching the underside of the hood. I’m not an electrical guy so I have no clue as to the science, other than that unwanted grounds are unwanted grounds.

I covered the battery post with electrical tape (the positive already had the factory cover) and I had no further problems.

@MysterYvil:

Regarding, the hood, wouldn't the hood already be grounded, assuming you had a negative ground electrical system?

Yes, the hood should be grounded. Maybe it was a positive ground car? After spending many years working on electrical systems, I’ve learned a few things: 1. If it ain’t broke, don’t fix it. 2. If you fix somehting and it don’t make no sense, but works better, don’t question it, just move on. It would be nice to get a text book answer on every single reason why something works or doesn’t, but since we cannot even agree on which way the electrons flow (neg to pos, or pos to neg), some things are better left alone.

That’s what I thought too, but as bennyandthejets pointed out, “2. If you fix somehting and it don’t make no sense, but works better, don’t question it, just move on.” And it’s worked perfectly now for avoer two years, so I’m happy. :slight_smile: