Post-battery death: what-to-do
09-09-2002, 12:36 PM
#1
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Post-battery death: what-to-do
Err...left my reading lights on for like 3-4 days and battery of course died (99 A8). Friend jump started car for me no problem. Left car idling (revved engine a little bit) for < 10 minutes with radio, A/C and headlights on.
Turned it off, and alarm works. Thought battery is fully recharged. Uh-uh, tried a day or two later but car battery had little charge, and I couldn't get engine to start.
So question is: Do you need to go DRIVE the car for like 45 minutes to fully recharge? Perhaps my idle-for-10-mins is way too little. ?
Turned it off, and alarm works. Thought battery is fully recharged. Uh-uh, tried a day or two later but car battery had little charge, and I couldn't get engine to start.
So question is: Do you need to go DRIVE the car for like 45 minutes to fully recharge? Perhaps my idle-for-10-mins is way too little. ?
09-09-2002, 12:45 PM
#2
If the battery was fully drained, it may be no good.....
but first jump start and drive the car (with as few electrical devices on as possible- no Ac, no radio, etc.) for at least 30 minutes. Highway driving would be the best, but only running your car for less than 10 minutes after full discharge is not enough. Good luck!
09-09-2002, 12:46 PM
#3
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It takes hours to recharge a dead battery
Your alternator was supplying mostly loads (A/C and lighting the big ones) at idle and couldn't recharge the battery.
If you were driving on the highway, it would take a couple hours to fully charge the battery. Ten minutes around town won't do it on a fully discharged battery. It will restore maybe 5% of its capacity which probably isn't enough to restart the car.
The best way to do it would be to get a 2 or 6 amp charger or so and leave it on over night. Even at 12 hours at 2 amps, that's only 24 amp-hrs, the battery is probably about 100 amp-hrs or more, so at two amps, it would take four days.
You didn't see anything unusual, it just didn't have a chance to charge.
pw
If you were driving on the highway, it would take a couple hours to fully charge the battery. Ten minutes around town won't do it on a fully discharged battery. It will restore maybe 5% of its capacity which probably isn't enough to restart the car.
The best way to do it would be to get a 2 or 6 amp charger or so and leave it on over night. Even at 12 hours at 2 amps, that's only 24 amp-hrs, the battery is probably about 100 amp-hrs or more, so at two amps, it would take four days.
You didn't see anything unusual, it just didn't have a chance to charge.
pw
09-09-2002, 06:18 PM
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Re: If the battery was fully drained, it may be no good.....
Yeah well the reading lights were both on for FOUR WHOLE DAYS so of course battery had no chance but to get to zero percent charge.
Ok I'll drive her around for a coupla hours no biggie.
Ok I'll drive her around for a coupla hours no biggie.
09-10-2002, 03:06 AM
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Some info
If you battery worked fine before this then with a good charge it should mostly recover. However there are a couple caveats.
Any lead-acid battery will accumulate a non-electrolyte coating on some of the plates each time the battery is at less than full charge, the lower the level, the faster this accumulation. It will eventually accumulate to the point where the battery will not sufficiently charge to start the car. It happens to most batteries eventually and is one of the biggest reasons batteries need to be replaced periodically.
So an older battery that experiences what yours has, may not charge back to sufficient levels to be dependable because of the accumulation.
Another problem that can develop with very low levels of charge is a cell short. This happens because the electrolyte changes states at very low charge levels and mineral crystals in the solution may settle out. Enough of them in theright place accumulate and a pair of adjacent plates will be shorted together preventing the cell from re-charging.
If your battery is a couple years old or more, once you have it charged back up, have it load tested to determine if it is strong enough to be reliable. Most places that sell quality batteries can do this. If it is not it will probably function in mild weather but fail you in extreme heat or cold weather just when you find it least convienent.
Any lead-acid battery will accumulate a non-electrolyte coating on some of the plates each time the battery is at less than full charge, the lower the level, the faster this accumulation. It will eventually accumulate to the point where the battery will not sufficiently charge to start the car. It happens to most batteries eventually and is one of the biggest reasons batteries need to be replaced periodically.
So an older battery that experiences what yours has, may not charge back to sufficient levels to be dependable because of the accumulation.
Another problem that can develop with very low levels of charge is a cell short. This happens because the electrolyte changes states at very low charge levels and mineral crystals in the solution may settle out. Enough of them in theright place accumulate and a pair of adjacent plates will be shorted together preventing the cell from re-charging.
If your battery is a couple years old or more, once you have it charged back up, have it load tested to determine if it is strong enough to be reliable. Most places that sell quality batteries can do this. If it is not it will probably function in mild weather but fail you in extreme heat or cold weather just when you find it least convienent.
09-10-2002, 05:57 AM
#6
AudiWorld Super User
Coming from an Ex Navy Electrician with more than enough experience with batteries....
....nicely said.
I use to take care of a 126 cell battery on a submarine, talk about a royal PIA! Try taking specific gravities of all of those cells laying on non conducting plates right above them with as little as 2 feet overhead space above that after doing an equalizing charge! Not fun.
I use to take care of a 126 cell battery on a submarine, talk about a royal PIA! Try taking specific gravities of all of those cells laying on non conducting plates right above them with as little as 2 feet overhead space above that after doing an equalizing charge! Not fun.
09-10-2002, 08:24 AM
#7
That's why they're called grunts...... ;-D
I've done my fair share of grunt work through the years too!! I didn't want to go into all the detail that WClark did, but he is absolutely correct.
