electrical problem - losing charge in battery

[Dave]

I don;t drive the cab that often. It has developed a habit of eating batteries - not just running them down, but damaging them to the point that they will no longer hold a charge.

If I drive the car consistently a few times a week, it doesn't happen. Its only after the car sits a while. Now I know that BMWs do trickle some charge off the battery (hence the battery tender that the dealer and other places sell.)

What I need to know is if it is normal not only to discharge the battery, but render it so it will no longer hold a charge?

I have replaced 4 batteries (all but one under warranty) because of this in the last 2 years. The latest today. Every time it has not only been discharged, but cannot be recharged.

[DarkWing6]

If you don;t mind resetting the clock you should unplug your battery when you are gonna let the car sit. It's probably easier to reset the clock than put in a new battery.

[Dave]

If you don;t mind resetting the clock you should unplug your battery when you are gonna let the car sit. It's probably easier to reset the clock than put in a new battery.

Yes, That's true. I am trying to determine if it is normal that the battery is not only discharged, but also left so that it cannot be recharged.

[Brew]

How long does the car go without being driven? It is normal for batteries to drain when they sit for long periods of time, and when they do they break down internally. If you know that you won't be driving it for a while (more than a couple weeks) you should pull the battery and keep it inside hooked up to a battery tender, which will maintain its charge.

[EtaSport]

Check to see how many amps are being pulled while the car is just sitting. I had this problem with my car when I got it, and it was draining the battery in about a week. When I removed the radio with the anti-theft I never had the problem again. In the end I still put a new battery in it, been going for 2 years. I'm not sure what else may stay on in your car, maybe security system, or if you do still have the radio in it, might be that.

[JeffG]

Like others have suggested already, check for any parasitic draw. Hook up a meter in series with the battery and read how many amps are being drawn. I'm not sure exactly what a good spec for E30's is, new BMW's have a window of 20-50mA or so before it is deemed excessive, so you'd probably want to have something around there. If you see you have a large draw, pull fuses one by one until you see the draw drop, then narrow it down from there by checking items that run off that particular circuit. This has worked many times for me successfully. Hope that helps some.

-Jeff

[bimmer8604]

Like others have suggested already, check for any parasitic draw. Hook up a meter in series with the battery and read how many amps are being drawn. I'm not sure exactly what a good spec for E30's is, new BMW's have a window of 20-50mA or so before it is deemed excessive, so you'd probably want to have something around there. If you see you have a large draw, pull fuses one by one until you see the draw drop, then narrow it down from there by checking items that run off that particular circuit. This has worked many times for me successfully. Hope that helps some.

-Jeff

i concur.

you're correct about the 50mA draw, no car should be drawing more than 50mA.

Dave, also check your terminals, i doubt they are corroded since you seem to be having to change batteries so often, but next time your battery dies, check the water fluid, and put it on a slow charge, 5ams for about 30 hours. should break the sulfer on your plates.

Kyle

[Dave]

Like others have suggested already, check for any parasitic draw. Hook up a meter in series with the battery and read how many amps are being drawn. I'm not sure exactly what a good spec for E30's is, new BMW's have a window of 20-50mA or so before it is deemed excessive, so you'd probably want to have something around there. If you see you have a large draw, pull fuses one by one until you see the draw drop, then narrow it down from there by checking items that run off that particular circuit. This has worked many times for me successfully. Hope that helps some.

-Jeff

i concur.

you're correct about the 50mA draw, no car should be drawing more than 50mA.

Dave, also check your terminals, i doubt they are corroded since you seem to be having to change batteries so often, but next time your battery dies, check the water fluid, and put it on a slow charge, 5ams for about 30 hours. should break the sulfer on your plates.

Kyle

Thanks for the ideas, guys. Got a new one in there. I am going to check the draw, and my first suspicion would be the radio - it has an aftermarket head unit that is "creatively" installed.

[Budget Beater]

could possibly be lights being left on (aka glovebox light b/c glovebox not closing completely and making full contact or etc). if so you may want to consider LED based interior bulbs, they are like $5 a pop on ebay. they use nearly 90% less electricity and are brighter and true white light (vs. orangy stockers). I did it in my E36 M3... did wonders. I ran super lightweight odyssey battery and had zero problems.