Battery continues to die

[bradbig]

Hi guys. I'm at my wits end. My 73 Fiat Spider has had the same problem since I bought it 3 years ago. The battery dies, from fully charged, to almost dead within 3-4 days, completely flat after 5-6 days or more. I'm on my second brand new battery. So far: battery tests 100% charged, alternator charging is within parameters (steady at 13.75 volts), alternator draw test (10 amp) gives correct response, battery draw test (10 amp) gives correct response, test for parasitic current drain shows only .22 of an amp (tested this at least 10 times, at different times, for short tests, long tests leaving the meter on for a few hours to watch for any change). So, battery is new, alternator output and charging are correct, typical current drain with engine off (clock, stereo, alarm, etc.) is within normal parameters at .22 of an amp, yet the battery continues to die. I cannot figure it out. The first battery I took back to the place that I bought it, and the gent put a very sophisticated tester on it and said "yes, it's bad" and replaced it with the one I have now. Is it possible I've had two bad batteries in a row, or am I missing something obvious? Any help would be appreciated, greatly. Thanks.

[narfire]

My battery was dying after 3-4 days as well. I put a multi meter on the stud on the alt and it was reading 9.4 V at 2500 rpm. swapped out the volt. reg and all is good now (14.2V). Your alt is showing 13.74 so I really don't know why it would be draining like that.
When I had a fully charged battery I did have 12.6 showing at the stud.
Perhaps next time you have a dead battery, bump start the car and then check the alt. I did and that is when I had 9.4 V showing.

[bradbig]

Yes, it is puzzling. If the battery takes a charge, and the alternator is putting out the correct voltage and isn't overcharging and there isn't a problematic parasitic current drain when the vehicle is sitting with the engine off, why does my battery keep dying? I just can't understand from a technical/mechanical point of view how it could even happen, and I'm on my second, brand-new battery.

[spider2081]

I believe 13.75 volts is the minimum your alternator should be putting out. An old rule of thumb was 13.75-14.5 volts with everything in the cars electrical system on. Thats all lights and fans on and engine RPM 2500-3000 measured at the alternator output post.
Remember there are 3 sets of diodes in an alternator. If one set is defective and the other two good an unloaded alternator will still put out about 14 volts. The voltage will not decrease until the demand on the alternator exceeds what the 2 remaining sets of diodes can produce.
Also 0.22 amps or 220 milliamps is high for a constant parasitic draw. That is about what one of the light bulbs in the instruments draws.
I think you need to identify what the draw is on the battery. Also I would have the alternator and regulator tested by a local shop that specializes in auto alternators and starters.

[bradbig]

With the engine running at idle speed and nothing on, the alternator puts out about 13.75 volts. With a 10 amp load on, the output voltage drops to about 12, then comes back up to 13.75 when the 10-second, 10 amp test is done.

[bradbig]

I was told, and have read, than parasitic drain from clocks, radio, etc, between .18 and .25 of an amp isn't uncommon and isn't near enough to kill a fully charged battery in 3-4 days. When I open a door, say, the amp reading jumps to about 1.5 amps.

[DieselSpider]

What brand of battery are we discussing here. Walmarts house brand "Never Start" can be very iffy so with that brand it would be quite possible to get two bad ones in a row. With multiple cars in the drive though I would swap batteries with another vehicle that has not exhibited this issue and if that vehicle inherits the problem when the battery from the Fiat is in it then your chances are you need to find a better source of batteries.

Even if you are not seeing a parasitic draw there is still a chance that some batteries will drain power from the case sitting on a metal tray. Some find that a plastic insulator under the battery and hold down clamp mitigates this. A dirty battery can also leak current due to the dirt especially if its damp or humid.

[bradbig]

It's an Interstate battery, very clean and new, the second one in a row. I may try disconnecting the negative cable entirely, and let it sit for several days, and see what happens to the voltage. If it dies, then I'll know it's the battery, if it's still good, then I'll know the car is still draining current.

[spider2081]

I may try disconnecting the negative cable entirely, and let it sit for several days, and see what happens to the voltage.

Good thought

[DieselSpider]

Interstate should be good unless the dealer is cleaning up old ones and putting them on a de-sulfating charger then labeling them as new. Some Sears stores would do this with their batteries.

Any chance that the cooling fan is cycling on while its sitting? That would drain things too and you'd have to catch it when its happening to know about it unless you have a current draw meter with a time recorder.

[bradbig]

I don't think I'm getting reconditioned batteries.

I've never heard the cooling fan come on while the engine is off, and it's parked near my other vehicles, so I'd hear it if it did. That having been said, I've thought that it almost seems like something is coming on intermittently while the engine is off, but I can't think of what it might be.

Disconnecting the negative cable should tell me whether it's a battery or a current drain issue.