Question:

1986 bmw 80,000 original miles. keeps "killing batteries"

by Guest7180 | 12 years, 7 month(s) ago

What "simple" problem would cause batteries to go completely dead after few weeks/months? Replaced alternator and battery December. I did leave lights on til it was totally gone. Fiorst time, took immediate charge. two weeks later, killed battery again, my fault. would not take charge. took to mechanic, he said he put new cable in/on. car drove two weeks, dead again. Please, please don't tell me it's starter! When battery is fine, car always starts immediately. what can i check/how, cost? i hope you can help me. thank you,very much. mimi

Tags: 1986, 80000, batteries, BMW, Killing, miles, Original

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Guest5534

Mimi, I had a 1983 Bavaria with a similar problem. Here's how we isolated the problem:

    Disconnect the wire from the positive terminal that goes to the starter solenoid(usually a fairly heavy red wire). Then disconnect the battery positive terminal at the battery, and hook up a cheap DC ammeter (available at discount and auto parts stores for about $20) IN-LINE between the battery terminal and the cable end. You will probably see a reading in the neighborhood of >= .05 amps. If not, it IS the starter (probably the starter solenoid).

    If you DO get the above reading, have someone watch the meter while you pull out the fuses in the glove box, one at a time. If the meter goes to 0 (zero) amps when you pull out a specific fuse, the problem is either a short circuit or bad component on that circuit. At that point, a good repair manual (again, about $20 at an autoparts store) will help you in determining what is on that circuit, and the wire colors involved.

    By the way, I had a shorted high-speed resistor in the heater fan which was running my battery down. I bought a whole assembly for $10 from a junk yard - Problem Fixed!
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