How long to charge a car battery

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Old 01-08-20, 10:36 AM
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How long to charge a car battery

I was wondering how long I should charge my car battery to get it to full charge (12.66v). The battery is at 12v after resting overnight. I have an 8 amp charger. I don't want to overcharge the battery. The battery was at about 12.35v before I replaced the alternator which died and drained the battery.

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Old 01-08-20, 11:50 AM
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Depends

A trickle charger would take longer but the newer ones monitor the voltage and shut themselves off when fully charged, safest way.

The larger chargers are typ dumb chargers and I would not leave them on for extended periods unattended.
 
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Old 01-08-20, 12:02 PM
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If you will be driving the car on anything other than a short trip, you just need it charged enough to start the car. Your alternator will take care of the rest. If the battery continues to not take a charge, the battery needs to be replaced.
 
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Old 01-08-20, 12:41 PM
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You can get a very rough estimate of charging time if you know the size (amp capacity) of the battery. Obviously a large capacity battery will take longer to charge than a small one.

One way I tell is by keeping an eye on the charging rate. A more deeply discharged battery will suck up the full 8 amps your charger can provide but as the battery approaches being charged the amperage will drop. If the battery has a partial charge it may only take 4 or 6 amps when you hook up the charger. If you check back in an hour or two and it's still taking about the same amperage as it did when you started you know you are still a ways from being charged. But, if the amperage has dropped significantly you know a full charge is much closer.
 
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Old 01-08-20, 07:21 PM
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Depends on battery size, clearly.
fully charged battery should show around 14V. 14+.
Your battery is not charging properly or does not hold charge.
Even deep cycle battery I had fully charged overnight and they take A LOT of charge.
 
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Old 01-09-20, 04:06 AM
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There are slightly different recommended fully charged voltage levels but the generally accepted minimum is to charge to 14.2 volts dropping and holding a steady 13.8 volts.
Also not universally agreed the full range would be 12.8 volts as fully charged and 11.8 volts as fully discharged.
One thing is for sure and that is if you don't charge to at least a steady state of 12.8 volts your battery is not fully charged.
One way to get a clue as to your batteries condition is to charge to 14.2 volts and let sit for 24 hrs.
The voltage should not drop to below 12.8 volts.
 
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Old 01-09-20, 06:27 AM
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How old is the battery?
Most decent battery chargers will shut themselves down when the battery is recharged.
 
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Old 01-09-20, 08:49 AM
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I'll try a 12 hr charge. I bought the car 1 1/2 years ago and have no idea how old the battery is. Although it looked pretty new.

Thanks for all the info.
 
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Old 01-09-20, 10:11 AM
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You can take it to almost any auto parts store and they can load test it for you.
 
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