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1/25/2018 7:38:29 AM
Posted: 3/28/2006 4:36:43 PM EST
I believe I'm having battery trouble.

Took the Interstate battery in to the closest guy (a body shop). He tested it, came back as "Charge and re-test".

He charged it (said it went through several charge cycles), and now it tests fine. He is going to have the interstate guy take a look at it tomorrow on when he comes by.

When I had it in the car, regardless of how long the car was running, it wouldn't pick up enough of a charge to start the car. I had also run the home (2/10/50 amp set on 10 amps) charger for several hours on it with no real success.

When I did the testing it tested at about 12.4 volts. Drops to 8 volts after it struggles to start the car. Letting the battery sit for a while (unplugged from the ground in the car), it would drop about 0.3 volts overnight.

When the car is running, I get about 13.5 volts with the lights on, fan blowing, etc.

What is normal alternator output at idle? What about with multiple accessories on?


(Car is a BMW 318is 1991).
Link Posted: 3/28/2006 7:25:43 PM EST
sounds about right, my only experience is with my truck. It puts out around 14 volts loaded down.

Sounds like your battery is buggered to me. I've had bad luck with batteries in a series of vehicles... I don't hesitate to drop in a new one.
Link Posted: 3/28/2006 7:45:26 PM EST
[Last Edit: 3/28/2006 7:48:41 PM EST by 69CougarXR7]
How many amps was the starter drawing when starting the car, how many amps was the alternator putting out, did you check the diodes? 13.5 is a little low, should be 13.8 volts. Have you made sure the connections were clean and tight. Are the cables/ends in good condition. Did the battery have any dead cells.

If the starter is bad it will draw too much current and eventually will kill the battery.

I know too many questions but check it all out, these problems are a pain in the ass and can be expensive replacing crap until you find whats causing the problem.

ETA: Most alternators will say on them somewhere how many amps it is supposed to put out. If not a quick call to the dealer should get you an answer. I would guess somewhere in the 80amp range.

Good luck
Link Posted: 3/28/2006 7:48:35 PM EST

Normal system voltage varies somewhat with weather. 13.8 volts is "normal", although up to 14.5 volts in cold weather and down to 13.5 volts in hot weather is also normal.

Where are you measuring the battery voltage? Have you checked the condition of your battery cables, especially the main ground? I have seen main ground cables, attached to the engine block, corrode from the inside out due to water that wicks its way under the insulation. Aside from charging system problems, the first clue that anything is wrong is when the cable is dangling there in the breeze.

Link Posted: 3/29/2006 3:57:19 AM EST
Does the battery pass a load test?
Link Posted: 3/29/2006 4:00:14 AM EST

Originally Posted By INI:
Does the battery pass a load test?

+1 sounds like you have a dead/bad cell.

Link Posted: 3/29/2006 11:53:48 AM EST
Interstate guy checked the battery and said it tested fine. The body shop guy will re-charge the battery. Once I get it back next week, I'll test it and see what I can come up with on readings while it is in the car.

I'll re-post when I get more information.

Link Posted: 4/8/2006 6:26:42 PM EST
Hooked up a temporary battery today (not able to get to the shop before it closed to get the Interstate battery).

My Alternator outputs at 13.85 volts (measured at the battery cables--the battery is in the rear of the vehicle) while running. This appears stable regardless of the RPMs of the engine.

Under load (lights and AC on, door open with door chime going off, fan blowing full in the car), it drops a bit to about 13.7 volts.

Still above normal battery voltage (12.9)--so it should be charging, correct?

Link Posted: 4/9/2006 5:19:39 AM EST
above 12 is ok.

If the battery passes load test, and the alternator is charging, it's time to test the vehicle for a parasitic drain. You may have a short or faulty component in the system somewhere.
Link Posted: 4/9/2006 7:55:07 AM EST

Thought of that already--I had the problems even after I had installed a battery disconnect (flat plate on the battery terminal connector to flat plate on ground wire--connects via heavy duty screw with twist knob on top).

Link Posted: 4/9/2006 1:30:35 PM EST

Originally Posted By AFARR:

Thought of that already--I had the problems even after I had installed a battery disconnect (flat plate on the battery terminal connector to flat plate on ground wire--connects via heavy duty screw with twist knob on top).


If that battery is discharging even with it disconnected......replace it.
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