Why was my battery dead?

[DavidH]

My battery totally ran down and I can’t figure out why. Here’s the facts:

1. It's a ‘91 Spider.
2. New Optima Red battery.
3. One year old Hella halogen headlights.
4. Drove the car for three hours today.
5. Ammeter on dash always showed charging at ~14 volts.
6. At end of drive I turned off the engine and left the headlights on for about fifteen minutes. When I tried to start the car, the battery was dead.
7. I don't know of any shorts or phantom power drains in the car (well, there's the clock).

Any ideas? Can a new battery really run the headlights for only fifteen minutes or so? Thanks very much, everybody.

[ghnl]

Were you trying to re-start the car after leaving the headlight on for the 15 minutes - or did you shut off the lights after the 15 minutes but then didn't actually try re-starting it until some time much later (like many hours or days)?

If the former then I'd be puzzled. It would seem like any decent battery would not go totally dead from powering the headlight for 15 minutes.

If the latter then I think it is more likely there is a significant electrical drain somewhere. (A radio memory or clock should not be a significant drain.) Does your Spider have the footwell interior lights? They have a 3 position switch - auto (on with door open), off, & always on. Sometimes it gets kicked to the 'always on' position. That could drain the battery in a few hours.

[msiert]

I had a slow drain on my Spider but in my case I would leave the radio on for a while after slutting the car down. Never did find it might be fixed now sence I switch out the ecu and FI system but have never tested it.

The guy that installed the new ecu said that he found my slow drain problem when he was installing it (which I complained to him about) but I never did ask him what he found.

I have a battery cut off switch that I shut off after each drive so it's not an issue with me anymore.

[Incompatible]

5. Ammeter on dash always showed charging at ~14 volts.
The spider does not have a Ammeter ! but a voltmeter.

This gauge does NOT show if the battery is charging but shows the output voltage of the alternator which in theory should be the same voltage as the battery ...
Thus, even if you would disconnected the battery while driving, this voltmeter will show in-between 13.7 ~ 14.7 volts @ 3000 RPM
So when your voltmeter shows 14V on your dash, this does not mean that your battery is properly charging!

Double check the ground connection of your battery !!!

If in doubt that you battery does not charge, Pepboys or NAPA both sell a cheap under the dash Ammeter (this gauge usually measures in-between +60 to -60 Amp)
Connect this gauge in SERIES and is very helpfull in troubleshooting

Good Luck

[DavidH]

THANKS, everybody.
Eric, I turned off the lights, then immediately tried to start the car. I do have footwell lights, but they really do turn off about twenty seconds after the door closes. Does it sound like the battery might not be getting a full charge from the alternator? If that's the case, why and what to do about it? Could it be as simple as a weak ground connection to the battery, as Incompatible suggests? I'll pick up that "cheap ammeter" and see what I find. Stand by...film at eleven.

David

[andytitterton]

Whether your battery is charged or not, a bad earth connection will give you poor starting symptoms. Try a voltmeter across the battery terminals. It should show about 14V at 3000rpm if charging OK.

With regard to leaving your lights on, since a 60W headlight bulb equates to 5A, you will be drawing 10A for both headlights plus about 2A maximum for everything else (rear lights etc). Assuming your battery is 50Amp/hour, you should, in theory, have 4 hours approximately of power for leaving the lights on. If you have a 60A/H battery, you should get 5 hours, but even so, to leave the headlights on for 3 hours may be pushing your luck a bit.

(60Amp hours = 60A for 1 hour, 30A for 2 hours, 12A for 5 hours and so on)

[msiert]

Quote:

Originally Posted by andytitterton Whether your battery is charged or not, a bad earth connection will give you poor starting symptoms. Try a voltmeter across the battery terminals. It should show about 14V at 3000rpm if charging OK.

[aldo]

Davis,
How old was your previous battery and why did you replace it.
Could be the problem proceeded your current battery.

[DavidH]

Aldo, Funny you should ask. The reason I bought the Optima was because it appeared that the previous battery (the one that the PO had put in the car) was not taking a charge. The previous battery ran down fast a couple of times under the same circumstances as I described in my first note above. So, I dont think it is the battery -- in fact, I probably didnt need to buy the Optima, even though it is a very good battery (likely better than the one that came with the car). Hmmmm.

[DavidH]

Could someone explain how to check whether the ground connection from the battery is good? Is it anything more than following the negative battery cable and making certain that it is securely bolted to the car frame? Thanks again.

[ghnl]

A visual check is usually not good enough. Better to dis-assemble each connection, clean the terminals and the connection area then re-secure. (a dab of di-electric grease is useful to stave off corrosion which is usually the problem with iffy connections)

If you wanna get fancy you can do a voltage drop test with a simple voltmeter. Here's the explanation of how to do that from my brother's web page: chasing sparks

[andytitterton]

I have a similar problem on my Series 3 - If I leave the battery connected, it goes flat within the week. I suspect it must be leakage somewhere, so I will be checking each individual circuit with an ammeter as well as the main feed to the battery. It could be a leaky diode in the alternator, a problem I've previously experienced on another car (not an Alfa).

I wish you luck in finding your problem, and if I find mine first, I'll gladly let you know.

Our problems will not be due to a faulty earth on the battery though. You won't even turn the engine over with a bad battery connection!

One more thing - If the voltmeter is showing 14 Volts, the battery will be charging. Whether the battery has a fault such that the charge is not retained is another matter.

[papajam]

I've found that S3 and S4 Spiders are notorious for charging circuit voltage drop. Please give this post a read.

[lowmileage]

Quote:

Originally Posted by Incompatible [color="Red"] Pepboys or NAPA both sell a cheap under the dash Ammeter (this gauge usually measures in-between +60 to -60 Amp) Connect this gauge in SERIES and is very helpfull in troubleshooting

[DavidH]

more thanks, everyone. I plan to run the tests over the weekend and let you know what I find. If it always worked right, what fun would that be?