What could be draining the car battery and how can it be fixed?

[rprastein]

TL;DR Summary

Dead battery <1V voltage doesn't budge with jumper cables - what is mechanism?

Our car battery is past its warranted life by 1.5 years (it's 5 years old). It's been discharged a few times due to lights being left on overnight. We're not currently using the car because of engine issues, so it just sits in the driveway for the last few months. Last week, it was found discharged again, not sure why - maybe the thieves rummaging though our glove box the previous night left a door open when they were done. It took longer than usual to jump start it the next morning. Two nights ago, it was dead yet again - the ominous, no sound at all and no accessories or dashboard lights when turning the key in the ignition, kind of dead. The next day, I checked the voltage across the battery terminals, and it was < 1V. I tried jumping it again, with a different good battery vehicle. I had a good jumper connection, with a spark when connecting the negative cable to the body of the car with the bad battery. Voltage across the bad battery terminals was still <1 with the jumper cables connected, and stayed that way for several minutes with the good car running. Never any sound with turning the key in the ignition of the bad car. I'm going to go get a replacement battery today.

Is this an indication of an internal short in the bad battery? A short somewhere else? There have been rodents under the hood, with feces and urine found on the top of the battery, as well as some newer corrosion. I cleaned the top of the battery with a brush before the second jump start attempt.

Is there any risk to the good battery/good car or the circuitry of the bad car when I try to jump a battery like this that won't even take a charge at all?

Thanks,

Rebeccah

 

[Baluncore]

Welcome to PF.

It could be a shorted battery or an open circuit cable or connector.
Get the new battery, but check all battery connections for corrosion and integrity before fitting it.

Car batteries die if they are left discharged, so put a solar battery charger on the vehicle to keep the battery charged while it is not being used.

 

[jack action]

Physically inspect the battery to see if it is swollen. This a good sign you need a new battery.

Is there any risk to the good battery/good car or the circuitry of the bad car when I try to jump a battery like this that won't even take a charge at all?

It's never a good thing to jumpstart a dead battery for the good battery. The worse is the condition of the dead battery, the worse it is for the good battery. In your case, I wouldn't recommend it.

 

[Averagesupernova]

TL;DR Summary: Dead battery <1V voltage doesn't budge with jumper cables -

You are missing something. You cannot have the reading you think you have unless you have a poor connection between the dead battery and the good battery. Depending on where you hook the jumper clamps, the connection could be a battery cable on the dead vehicle.

 

[rprastein]

"The connection could be a battery cable on the dead vehicle" - you mean the bad connection? I tried checking the voltage between the terminals of the bad battery, and also the voltage between the positive terminal and the body near where the negative cable was connected. Now I'm wondering if I just didn't have a good connection of the voltmeter itself, complicating things. Well, the battery needs replacing anyway, so I'll start withtaking the old one out, cleaning up the battery cable ends really well and checking (in daylight) for any obvious rodent damage to the wiring. I wish this car had a battery cover like my other one does.

 

[rprastein]

Welcome to PF.

It could be a shorted battery or an open circuit cable or connector.
Get the new battery, but check all battery connections for corrosion and integrity before fitting it.

Car batteries die if they are left discharged, so put a solar battery charger on the vehicle to keep the battery charged while it is not being used.

Thanks, Baluncore. I plan to give everything a thorough check now that it's daytime and I have some time. Solar charger is a good idea.

 

[Baluncore]

Maybe some of the diodes in the alternator have fused and shorted, because the jumper cables were connected backwards with a dead battery. That may give you a 1 volt battery voltage. Disconnect the thick alternator to battery wire to check for that high current draw.

There is a false economy, trying to work around an old battery can result in a cascade of problems. The alternator may suffer from inexperience, but I have known people with broken legs and ribs, crushed in the door while trying to push or roll start a car.

 

[Guineafowl]

I’ve seen plenty of old car batteries with <1 or 2 V on them. My smart charger looks for a minimum of 2V before it will start the cycle, so sometimes it’s necessary to ‘jump’ it with a 12v supply to get things going.

One cause seems to be lead shedding from the plates, which builds a layer of conductive silt at the bottom of each cell, shorting it out. The lead flakes may also get trapped between plates on the way down.

At the same time, sulphation on the plates hardens and robs capacity.

You can attempt recovery with a current-limited bench power supply, set to 1A, and about 24V. It will take perhaps hours, but eventually the charging current will increase. Leave the cells caps loose and be aware of the flammable vapours produced. Don’t leave it unattended. You may get some more life out of the battery but it’ll never be perfect.

 

[rprastein]

Maybe some of the diodes in the alternator have fused and shorted, because the jumper cables were connected backwards with a dead battery. That may give you a 1 volt battery voltage. Disconnect the thick alternator to battery wire to check for that high current draw.

There is a false economy, trying to work around an old battery can result in a cascade of problems. The alternator may suffer from inexperience, but I have known people with broken legs and ribs, crushed in the door while trying to push or roll start a car.

Yesterday, I cleaned off the battery cable ends and replaced the battery. I found out what drained the battery the last time. After jump starting the car the time before, the power door didn't work, and in the process of trying to remember what I had to do to reset it, I moved the dome light switch from "Door" to "On" - causing all of the interior lights to be on all the time until the battery was drained.