Stolen cars and dead batteries

blincoln

About three weeks ago my car was stolen. The thieves drove it off by breaking open the assembly where the key + cylinder turn and activate the ignition and accessory power, and turning the switch by hand or with a screwdriver or something.

When it was recovered a few days later, I had it taken to an impound lot because I didn't want to drive it anywhere with all that electric wiring exposed right above my legs. The accessory power was still turned on, and AFAIK the battery would have been drained while it sat in the lot. The next day I had it towed to the dealer where they replaced most or all of the steering column assembly. That was about two weeks ago.

Over New Year's weekend, the battery went dead. I tested it with my multimeter, and it came up around 2-3 volts. This is an 84 month battery I bought about a year ago, so I don't think it's its age. I double-checked to make sure I hadn't left anything turned on.

I know a bit about the mechanical workings of my car, but only a little about the electrical side - basically just enough to wire up a new stereo in it with an amp in the trunk a few months ago (which fortunately was left by the car thieves).

Before the theft, I hadn't had any problems with the battery after a regular weekend at least, so I assume I didn't screw anything up in terms of the stereo equipment.

So I can only think of three things that might be going on, and my car knowledge is limited enough that I don't know if either is possible or likely:

- While it was stolen, the alternator was damaged in some way by the screwing-about with the ignition.
- Being drained completely in the impound lot permanently screwed up the battery.
- Something has gone wonky with the amp, and its remote-on is being triggered even when the accessory power is turned off.

I'm charging up the battery now, so in the morning when I put it back in I can check the light on the amp to see if it's on all the time, but it doesn't feel like the cause to me, given that it worked fine before, the thieves apparently didn't even open the trunk, and there are some known bad things that happened to the battery and the ignition.

Aurin

If it's the same battery that was in it when it was stolen, it is more than likely the battery.

It also depends on the area that you live in as to how long batteries last. I can get about 1-2 years off of a Duralast battery in Arizona, but back home in Georgia I know they'll keep on going for a while.

It's also much easier and cheaper to replace a battery than an alternator, so best to go with cheapest options to work your way up to the expensive ones.

Thought Policeman

Unless I'm highly mistaken, a 12 volt battery at 2-3 volts is permanently damaged. I would reccomend getting a new battery, unless you are miraculously able to get that one to hold a charge. Then you will want to test your alternator while that car is running.

Blake T

If you know anyone with a car battery charger pop it on there for a while first and see if something is plain out draining the battery.

wmelon

you can also take your battery to an auto parts store. They can test to see if it's still good.

Ruckus

Even when "dead" a 12 volt car battery should produce much more than 3-4 volts. It you can, disconnect the battery and test for resistance between the chassis and red (pos) cable. With the ignition off, the resistance should register as nearly infinite (meaning no connection at all, just how you want it). If you get any insignificant resistance, or none at all (as in a short) disconnect your amp and try again. If you show that the amp isn't affecting it, take it to the dealer that replaced your column, leave your amp disconnected until they figure out where the short is.

Whenever I have to deal with a wreck or vechicle getting towed or impounded, I disconnect the pos battery cable and wrap it in duct tape. It keeps the battery from dying because of shorts and it also the first thing anyone logically checks if the car doesn't start, so it's easy to reattach.

Everywhereasign

I recovered a totally dead car battery last summer. We were on a fishing trip and had a spare.

The process involved making sure the liquids were topped up (it was a "regular maintence" type battery) and putting it on the charger. It maxed out really fast and the charger cut out. I d/c'd it and let it cool. Then charged it again. This time it charged for a little longer. This went on for about a week, charging once a day for a few hours. In the end it was back working fine and we never had any more problems with it.

All that being said, it was for power acessories on the boat, not the starter. I don't think I'd do that with my car, I like it when it starts every time.

blincoln

Ruckus wrote:

It you can, disconnect the battery and test for resistance between the chassis and red (pos) cable. With the ignition off, the resistance should register as nearly infinite (meaning no connection at all, just how you want it). If you get any insignificant resistance, or none at all (as in a short) disconnect your amp and try again.

I think we have a winner. Let me run this by you all to make sure I did it correctly, as it was the first time I've done electrical troubleshooting.

With the battery removed entirely (hooked up to the charger), I measured the resistance between the positive cable and the chassis in the engine compartment and got 1-2 kilohms. I removed the fuse that I'd put inline on the +12v line from the battery to the amp in the trunk and the resistance jumped to about 125 kilohms. That's not infinity, but obviously it's a lot higher so I assume the problem is at least related to the amp.

So to narrow it down between the amp and the wiring, I went into the trunk. The resistance between where the +12v line connects to the amp and the chassis (or alternately between the +12v and ground connections on the amp) is also about 1-2 kilohms. The resistance between the ground connection on the amp and the chassis is almost nonexistent, which I expected as the ground connection is just a ~meter-long wire from there to the chassis.

To make absolutely sure there wasn't a short in the +12v line, I pulled the fuse that's in the amp itself, and was no longer able to measure resistance at all.

What this implies to me is that the amp is pulling power even when the remote on wire isn't live. Maybe a relay is stuck open? It's an older amp that I got for free from a friend, so it's not a huge loss if I have to replace it.

So did I get it right?

Ruckus

That sounds like it might be your trouble, but I'm not sure about the values (I'm not familiar with how much resistance should exist exactly).

One thing I would assume is that the amp should normally be wired through an accessory connection and not directly to the battery, so turning off the key kills power to the amp as well. It sounds like the power for the amp is directly connected to the battery.

blincoln

Yeah, when you wire up a power amp you have to connect its +12v directly to the battery, because it pulls too much current to run through the accessory circuit. I followed the recommended procedure, which is to put an inline fuse on that wire run right near the battery, so that if there's a short, it blows there instead of burning up the passenger compartment.

There is a third wire that connects to the amp from the accessory circuit (the "remote on" I mentioned) which is supposed to control a relay or whatever in the amp that makes or breaks the real +12v connection from the battery.

Thanks for your help!