How does the new electronic 12v car battery chargers work???

**broken link removed** Vehicle battery is only 6 months old. I parked the vehicle and left the RV plugged into the vehicle for 3 months. Everything in the RV is off, refrigerator off, lights off, hot water heater off, it is all off. RV has its own 12v battery it is only 1 year old it is dead too.

When we return from camping I usually remember to unplug the RV from the Chevy Tahoe. Chevy battery stays charged and RV always goes dead unless I plug an extension cord from the RV to the garage 120v that keeps the RV battery charged.

I have the battery charger connected to the Chevy Tahoe battery with RV not connected.

With battery charger on 50 amp charge is will charge for 1 second then turn off for 7 seconds, over & over & over. It will take a week to charge if the charger only stays on 1 second each 8 seconds.

With battery charger on 10 amps it charges for 3 seconds they turns off for 7 seconds, over & over & over. It will take a week to charge the battery if it only stays on 3 seconds of every 10 seconds.

With battery charger on 2 amps it stays on all the time. 1000 amp battery will take 500 hours to charge on 2 amps.

I need an old school battery charger that stays on.

The battery charger is Harbor Freight brand it has always worked good before but batteries were never completely dead.

**broken link removed**

Your auto parts store will test the battery. They will say the battery will not take a charge and needs replaced.

I was told, as a rule of thumb, leaving a lead acid battery flat for 1 day knocks a year of it's life. I'm guessing you need new batteries.

Mike.

For the winter I put a trickle charger on the batteries. I think it only puts 0.1 amp into the battery all winter long.

ronsimpson said:

For the winter I put a trickle charger on the batteries. I think it only puts 0.1 amp into the battery all winter long.

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I do the same thing. I had the RV plugged into 120 volts its battery charged that also keeps the Chevy Tahoe battery charged with the vehicle & camper connected. Someone mowed the grass removed the plug and never plugged it in again and I never noticed it. I started the vehicle about 1 month ago to experiment with the GPS. Vehicle started easy. Some time in the past 30 days batteries both died.

I think the Harbor Freight battery charger is worthless. 50a for 1 second vs 10a for 3 seconds vs 2 amp continuous. I have not checked voltage output because this high tech charger puts out no voltage to check with a meter. Soon as I connect it to the battery it detects a small voltage that triggers the battery charger to put out a voltage. Assuming it puts out 18v x 2a = 36w. I bet if I take this battery charger apart tomorrow I bet the transformer inside won't be larger than 40 watts. I need to know what kind of worthless junk I have before we go camping again tomorrow I take it apart to see what is inside.

It may the battery voltage goes to 18 or 20V in 1 second and the charger shuts off. (bad battery)
OR
It might be that the battery voltage is 3 volts and the charger knows the battery will never charge. (bad battery)
OR

gary350 said:

Harbor Freight battery charger is worthless

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What does the charger do on your car battery. (known good battery)

My Chevy Tahoe PPV police interceptor has 2 batteries, 1 for the tow trailer and 1 for the engine. I had the charger on the tow trailer battery it has a full charge that is why the battery charger kept switching from charge to full charge.

I woke up this morning it occurred to me while sleeping I am charging the wrong battery. I have only owned this vehicle 6 months I had no clue which battery was the engine battery. I put the battery charger on the other battery and the charger works exactly like it should on all 3 settings, 2a, 10a, 50a. After charging the battery on 50a for about 5 minutes engine started. While engine runs I took battery charge apart there is a 1500 w transformer inside that is why the charger weigh about 10 lbs. I put charger on battery charging 10a. I will let it charge for 2 days 48 hr x 10a = 480 amps that is about 1/2 charged. Not sure what size this battery is could be 800 or 1000 amp. I will look and see.

Good battery charger after all, it was fooling me being connected to a battery that was not dead.

I still don't know what AGM is on the battery charger? 2 choices, regular & AGM

gary350 said:

Good battery charger after all, it was fooling me being connected to a battery that was not dead.

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Good, you found the problem.

gary350 said:

Not sure what size this battery is could be 800 or 1000 amp.

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You want the ampere-hour rating, not the starting current rating.

gary350 said:

I still don't know what AGM is on the battery charger? 2 choices, regular & AGM

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AGM is an Absorbent Glass Mat battery.
They can operate in any orientation and are typically used in motorcycles and perhaps other small vehicles.
It requires a slightly different full-charge cutoff voltage compared to the regular vehicle flooded-cell battery.
So for you batteries you would use the Regular setting.

So what horrible affiance did I do?
I got more negative clicks this morning then in the last two years.
Please show me where I was wrong. I want to learn.

My better battery charges shut down when the voltage is too high. Either because the battery has high resistance (bad) or the battery is charged. (charged is what happened)
My new battery charges will not charge a battery with low voltage. It thinks there is a short in the battery. (bad) My old chargers try to charge a shorted battery but over heat and shutdown.
I thought the charger was good and wanted to see it on a good battery. (this is the case, good charged battery)

Ron, I think your analysis is right on the money. It's exactly how our "smart" charger works.

I also agree with your analysis Ron.

Newer chargers will always use some sort of microcontrollers, and the manufacturer may have decided to add protection features.
An very-low voltage may mean either a dead or shorted battery, and you want to avoid that.
Additionally an overvoltage condition might mean that the you are attempting to charge a different voltage rating battery.

Old school chargers might create hazardous conditions. I personally witnessed an severely overcharged battery in a closed garage. Upon entering the garage, one would feel like a knife going thru the nose, and immediately started to gag.
The sulfuric acid had boiled out and created a poisonous atmosphere.

I will take a smart charger anytime.

ronsimpson said:

So what horrible affiance did I do?
I got more negative clicks this morning then in the last two years.

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Mine was just a mistake. thought I gave you an agree but must not have been directly over that icon. Sorry. It's changed now.
I have a couple of these smart chargers, and have had to trick them a couple of times by using jumper cables to the dead battery and a running car. I think if the battery is somewhere under 10V it won't charge.

And the 50amp won't work unless the battery is fully charged.