Charging battery with battery charger?

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May 28, 2019
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Hello

I found the positive battery cable terminal loose on my vehicle, I guess the shop that worked on it last didn't tighten it down all the way.

I tightened the cable terminal and drove the car a good bit however want to put a battery charger on it.

I have a 4 amp charger and the instructions mention something about when the charging current reaches about half the current value compared to when the charger was first connected that the battery is charged.

So I just connected the charger and the charger was showing a little over 4 amps. Should I disconnect the charger when it gets to 2 amps half that value? Or let it continue charging until the current gets close to 0 amps?

Thanks
 
Let it charge to 0. It charges full output until the battery gets to around 80%, then slows down to trickle it the rest of the way, hence the current drop. The battery gets a fuller charge with less current as it gets closer to full charge.
so before I connected the charger the battery resting voltage was 12.1V. I Connected the 4 amp charger and it was showing it was charging a little over 4 amps, at this time I measured the battery voltage (with the charger connected and it was about 12.9V. I continued to let it charge for a few hours and as the current on the battery charger went down the voltage at the battery with the charger connected and charging was going up. When the current got down to about 2 amps or slightly less the battery / charger voltage was 14.85.

I read that a EFB battery shouldn't be charged at a voltage higher than 14.5 V so I turned it off and then measured the battery resting voltage at is was 12.6.

I'm about to go to bed and I don't want to leave it on overnight.

Should I leave things as is? Or in the morning should I connect up the charger?

I am afraid if I leave the charger on until the current goes to 0 that the voltage of the charger output will be much more than 15V and maybe even 16 or more?

ideas?
 
I read that a EFB battery shouldn't be charged at a voltage higher than 14.5 V so I turned it off and then measured the battery resting voltage at is was 12.6.
In general, that is true. Overcharging is not a beneficial to any battery.

However, there is a time where final charging voltage must be high. When restoring an AGM or EFB, the method is to draw it down to 9V over a long period of time so all cells are low, then Constant Current charge at 1/10 the 1C (1 hour C rate) for 16 hours. Voltage will end up over 17V. This gently removes sulfation and can restore a fairly young battery in decline, such as one that was drained and underperforming.
 
Leave it be. Your 12.6 volts reading indicates battery is fully charged now.
I left it last night with the charger disconnected, the resting battery voltage was 12.7V, this morning I just checked and the resting voltage is 12.47V. So the resting voltage went down 0.13V.

Is this normal?

The vehicle is a 2021 RAV4 gas (non hybrid), with Start Stop so it has a EFB battery.
 
In general, that is true. Overcharging is not a beneficial to any battery.

However, there is a time where final charging voltage must be high. When restoring an AGM or EFB, the method is to draw it down to 9V over a long period of time so all cells are low, then Constant Current charge at 1/10 the 1C (1 hour C rate) for 16 hours. Voltage will end up over 17V. This gently removes sulfation and can restore a fairly young battery in decline, such as one that was drained and underperforming.
so should I put the charger back on it?
 
so should I put the charger back on it?
Yeah, you can reconnect the charger, mebbe for 2-3 hours. 2 amperes for 2 hours won't really overcharge the battery. Is the battery connected to the car? If it is, the computer sucked up some of the surface charge, thats why the voltage decreased. Good idea to measure the voltage every 15 minutes or so. I'd remove the charger when the voltage goes up to 14.7 volts. Any higher and the car electronics may get damaged.
 
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Yeah, you can reconnect the charger, mebbe for 2-3 hours. 2 amperes for 2 hours won't really overcharge the battery. Is the battery connected to the car? If it is, the computer sucked up some of the surface charge, thats why the voltage decreased. Good idea to measure the voltage every 15 minutes or so. I'd remove the charger when the voltage goes up to 14.7 volts. Any higher and the car electronics may get damaged.
Friday evening when I had the charger on I removed the charger when the voltage was 14.85V
 
You did fine, let it be. Since your car was starting with the loose terminal it was also charging. You just took it a little farther than the automatic process does... which is a helpful periodic battery maintenance thing for desulphation. Now you're done. Do it again in three months if it pleases you.
 
That is an old, manual charger. You need to monitor with that type. Don't just leave it unattended for long periods or you could overcharge.thaks

what do I monitor?

The voltage or the current? And when do I turn it off?
 
for reference here is the operating instructions for my charger the model number is A6612

See section 9 on page 4



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what do I monitor?

The voltage or the current? And when do I turn it off?
When using a manual charger, you should monitor voltage, current, and battery temperature. Stop charging at 0.5A, or higher if the battery temperature has risen more than 5degF. Charging voltage should not exceed 14.4V (at battery temp of 77F).

Or buy a modern automatic charger.
 
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