How long to drive to recharge battery?

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FCD

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One of my neighbors has a VW Lupo 1.2 or 1.4 her battery was flat so i jump started her car and she said i could go for a drive to re-charge it, i drove it for about 35 minutes and did about 40 Km ( 25 miles ) , on the highway with the engine at about 4k rpm, Would that be enough to re charge it to some extent so it'll start next time?
 
Agreed with above. Also batteries just dont go flat (as long as it wasnt just sitting for a long time), i would diagnose that as well.
 
Agreed with above. I get the impression it takes about 18 hours of driving to fully recharge a battery. Not a good way to recharge.
 
1) Drive a couple miles up to the store
2) Buy a battery charger
3) Return home. Charge battery.

You will never get a proper charge out of an alternator. Ever.
 
Originally Posted By: bubbatime
1) Drive a couple miles up to the store
2) Buy a battery charger
3) Return home. Charge battery.

You will never get a proper charge out of an alternator. Ever.

"puts on the humble hat"
guilty as charged.
OP, it happen to me, drove 2 hours, then didn't touch the car for 1 week = battery dead /empty

left it on the charger all night = happy in the morning
 
The problem was her daughter left the headlights on , when i came back and shut it off i started it again and it started ok, i wasn't looking to fully charge the battery just get it to start next time
 
Buy a charger at least and spend a few extra bucks for a smart charger. They have a renewal mode that can bring an old battery back to a bit more life.
 
If the battery is almost flat you could nearly buy a new battery in what it would cost in fuel to charge it fully by driving the car (UK fuel prices).

Driving it just far enough so that it starts OK and equating that with the battery being charged is probably responsible for shortening the life of thousands of batteries. Fine to get mobile again but asap the battery should be put an a charger until it's fully charged to prevent permanent sulphation damage. Amd that can take time. My car has an 85 AH battery. On a small bench charger it would take several days to fully charge that battery from flat.
 
The typical lead acid battery is about 70% efficient. If it's a 100 amp hour battery, about 140 amps for an hour is required to fully charge it. If your vehicle has a 100 amp alternator you can do the math. Be sure to add some compensation for the portion of the alternator output used to run the vehicle electrical system. There's no reason why the voltage regulator in a good alternator can't fully charge a battery.
 
A severely discharged lead-acid battery won't accept full charge current. Lead-acid batteries with even a few months of service show reduced charge acceptance (this causes problems with implementing automatic start/stop systems). For good life a lead-acid battery should be charged at .1C or 1/10th of it's AH capacity. .2C Therefore a 100ah battery should be charged at 10 amps.

http://batteryuniversity.com/learn/article/charging_the_lead_acid_battery
 
You're fine. There's car care then there's over-the-top car care.

My boss drove his junky sunfire on a bad alternator until it stalled out dead. He ignored the headlights getting dimmer and dimmer.

I fixed it on the side of the road, jumped it, and drove it 5 miles/ 15 minutes back to work. Turned it off, it turned back on. He gave me a ride back to my car and drove off into the sunset.

Alternators have temperature compensation so they overcharge for a couple minutes when cold. Your neighbor will rather quickly fill the battery up to 80% as its internal resistance is less when discharged, and then "top off" the rest with her alternator in fits and spits.
 
Originally Posted By: eljefino
You're fine. There's car care then there's over-the-top car care.

My boss drove his junky sunfire on a bad alternator until it stalled out dead. He ignored the headlights getting dimmer and dimmer.

I fixed it on the side of the road, jumped it, and drove it 5 miles/ 15 minutes back to work. Turned it off, it turned back on. He gave me a ride back to my car and drove off into the sunset.

Alternators have temperature compensation so they overcharge for a couple minutes when cold. Your neighbor will rather quickly fill the battery up to 80% as its internal resistance is less when discharged, and then "top off" the rest with her alternator in fits and spits.



That's blasphemy on BITOG!
smile.gif
 
The specifics of the chemistry, age, level of discharge, capacity to take a charge (all alluded to above) make for a complicated ballet.

BEST to put it on a good charger for a couple of hours and see what you got.

Flattening an old battery can always spell D-E-A-T-H.

...and that's about all we have time to deal with in the real world (where I spend the least amount of time as possible).
 
Just ran into this situation the other night. My wife's friend (lives in an apartment) accidentally bumped her headlight switch on while leaving the car. Later, the car wouldn't start. I jumped it, it started with little fuss. I told her to give it a high idle for as long as she could and left. My wife ran and got a couple of coffees and she and her friend had a coffee klatch for about an hour in her friend's car while the battery charged. I haven't heard anything back, so it must be OK. Sometimes it's not practical to hook up a battery charger and you do the best you can.
 
I've only swapped batteries a couple of times, but each time I didn't bother with a proper charger. 5 years on those batteries, which might have been shorter than the original, I'll have to admit. Then again, a "short" trip for me has always been less than a half hour; and most of the time an hour of driving is normal.

Might take longer to bring up to "full" charge, maybe it never gets to full, but IME it's been close enough.
 
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