Battery behavior

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Jan 3, 2006
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Location
Ohio
Hopefully somebody who knows lead-acid batteries and charging can shed some light on this. I've got a small 1.5 amp smart charger, and a 10 amp old school charger that will easily overcharge a battery. My knowledge of charging 12 volt batteries is the smart chargers get them up to about 14.5 volts, and they can be floated at about 13.2 volts. Fully charged and sitting idle they sit at about 12.6 volts. The little smart charger follows that charging method.

So I have a two 6 volt batteries for the Lincoln. I had bought an Optima battery when I had to travel out to Arizona to see if I could get it running, since the one in it was dead as a doornail. Charging the Optima with the little smart charger (it does 6 volts or 12 volts), it follows the same pattern at half the voltage. I bought a replacement Duracell SLI2 from Batteries Plus, since that's what was in the car. The Optima unfortunately is much smaller physically, though it has 1000 cranking amps. The Duracell does fit the battery tray perfectly, though it's only 675 cranking amps.

Now the Duracell is behaving strangely compared to other batteries. The smart charger gets it up to about 6.8 volts and it won't go any higher. If I put the old school 10 amp charger on it, it will get up to 7.2 volts, which is where the smart charger would normally terminate. Trying to figure out whether it's having a problem or if this is just how it behaves. I assume it would charge like any other lead-acid battery.
 
Perhaps the so called "smart charger" ain't so smart when dealing with a 6 volt battery. My old air cooled VWs [with a 6V system] would run at just over 8 volts.
 
My exceptionally limited understanding, so take this FWIW.

a 12V battery is 6 cells at approximately 2.1V each, so 12.6V output (its not perfect and can vary).

A 6 V is 3 of the same type cells, so 6.3V. When you series 2 batteries you get the 12.6V.

So on the charging side you need an over-voltage, to get current to flow the wrong direction. This has to do with the resistance in the cells, so half the cells, half the resistance, half the over voltage.

So a regular car battery will charge at about 14 volts at the lowest, so I think in theory anything over 7 volts should charge a 6V battery, but it will be slow. Possibly the resistance in a 6V system is lower so maybe 6.8V will work. Have you tried it?

Have you actually measured the smart chargers output with an ohm meter, or are you looking at something its telling you? 7V vs 6.8V is a fairly small difference and possibly is within the error range of the display?
 
Now the Duracell is behaving strangely compared to other batteries. The smart charger gets it up to about 6.8 volts and it won't go any higher. If I put the old school 10 amp charger on it, it will get up to 7.2 volts, which is where the smart charger would normally terminate. Trying to figure out whether it's having a problem or if this is just how it behaves. I assume it would charge like any other lead-acid battery.
There's nothing wrong. You have two different types of batteries. The Duracell is a regular flooded and the Optima is an AGM spiral. I have 2 Exide Com 2 batteries born 06/18 and after being fully charged sit for weeks at 6.3 volts. I also have an Optima born 09/11 which sits at 6.29v for weeks after being charged. The SOH for all is 100%.

The CCA needed for your Lincoln is probably around 300.
 
Hopefully somebody who knows lead-acid batteries and charging can shed some light on this. I've got a small 1.5 amp smart charger, and a 10 amp old school charger that will easily overcharge a battery. My knowledge of charging 12 volt batteries is the smart chargers get them up to about 14.5 volts, and they can be floated at about 13.2 volts. Fully charged and sitting idle they sit at about 12.6 volts. The little smart charger follows that charging method.

So I have a two 6 volt batteries for the Lincoln. I had bought an Optima battery when I had to travel out to Arizona to see if I could get it running, since the one in it was dead as a doornail. Charging the Optima with the little smart charger (it does 6 volts or 12 volts), it follows the same pattern at half the voltage. I bought a replacement Duracell SLI2 from Batteries Plus, since that's what was in the car. The Optima unfortunately is much smaller physically, though it has 1000 cranking amps. The Duracell does fit the battery tray perfectly, though it's only 675 cranking amps.

Now the Duracell is behaving strangely compared to other batteries. The smart charger gets it up to about 6.8 volts and it won't go any higher. If I put the old school 10 amp charger on it, it will get up to 7.2 volts, which is where the smart charger would normally terminate. Trying to figure out whether it's having a problem or if this is just how it behaves. I assume it would charge like any other lead-acid battery.
I'm thinking low on water, or a bad cell.
 
There's nothing wrong. You have two different types of batteries. The Duracell is a regular flooded and the Optima is an AGM spiral. I have 2 Exide Com 2 batteries born 06/18 and after being fully charged sit for weeks at 6.3 volts. I also have an Optima born 09/11 which sits at 6.29v for weeks after being charged. The SOH for all is 100%.

The CCA needed for your Lincoln is probably around 300.
Aren't most automotive batteries flooded batteries? That's why I'm not understanding why the Optima IS behaving like the flooded batteries I'm used to (my RV battery, my motorcycle 6 volt battery, pretty much every 12 volt car battery I've dealt with), but the flooded Duracell is NOT behaving like them. The smart charger has no trouble charging the motorcycle's 6 volt battery or the Optima battery, it gets up to around 7.2 volts, then it goes into float mode at 6.6 volts, which is what I would expect since it floats 12 volt batteries at 13.2.
My exceptionally limited understanding, so take this FWIW.

a 12V battery is 6 cells at approximately 2.1V each, so 12.6V output (its not perfect and can vary).

A 6 V is 3 of the same type cells, so 6.3V. When you series 2 batteries you get the 12.6V.

So on the charging side you need an over-voltage, to get current to flow the wrong direction. This has to do with the resistance in the cells, so half the cells, half the resistance, half the over voltage.

So a regular car battery will charge at about 14 volts at the lowest, so I think in theory anything over 7 volts should charge a 6V battery, but it will be slow. Possibly the resistance in a 6V system is lower so maybe 6.8V will work. Have you tried it?

Have you actually measured the smart chargers output with an ohm meter, or are you looking at something its telling you? 7V vs 6.8V is a fairly small difference and possibly is within the error range of the display?
You don't measure battery charger output with an ohm meter. I'm measuring the voltage at the battery with a volt meter while it's charging. The only indications on the smart charger are that it's in charge mode or float mode. If the battery voltage drops below 12.6 volts (or 6.3) volts, then it goes into charge mode until it reaches 14.5 (or 7.25) and then it goes into float mode. When I put it on this Duracell, it stays in charge mode for days and never goes higher than 6.8.
 
My experience with "smart" chargers is they don't like anything other than a slightly depleted battery. They only like to maintain a battery.
 
Aren't most automotive batteries flooded batteries? That's why I'm not understanding why the Optima IS behaving like the flooded batteries I'm used to (my RV battery, my motorcycle 6 volt battery, pretty much every 12 volt car battery I've dealt with), but the flooded Duracell is NOT behaving like them. The smart charger has no trouble charging the motorcycle's 6 volt battery or the Optima battery, it gets up to around 7.2 volts, then it goes into float mode at 6.6 volts, which is what I would expect since it floats 12 volt batteries at 13.2.

You don't measure battery charger output with an ohm meter. I'm measuring the voltage at the battery with a volt meter while it's charging. The only indications on the smart charger are that it's in charge mode or float mode. If the battery voltage drops below 12.6 volts (or 6.3) volts, then it goes into charge mode until it reaches 14.5 (or 7.25) and then it goes into float mode. When I put it on this Duracell, it stays in charge mode for days and never goes higher than 6.8.
Do any of the cells in the Duracell bubble when charging at 6.8 for an extended period? One weak/bad cell can continue to pull current and prevent it from reaching the termination voltage. Also, what are the specific gravity readings? Is one cell lower than the rest?
 
Aren't most automotive batteries flooded batteries? That's why I'm not understanding why the Optima IS behaving like the flooded batteries I'm used to (my RV battery, my motorcycle 6 volt battery, pretty much every 12 volt car battery I've dealt with), but the flooded Duracell is NOT behaving like them. The smart charger has no trouble charging the motorcycle's 6 volt battery or the Optima battery, it gets up to around 7.2 volts, then it goes into float mode at 6.6 volts, which is what I would expect since it floats 12 volt batteries at 13.2.

You are right most car batteries are flooded, but some are AGM Flat Plate or AGM Spiral (like the Optima). If you load test a Spiral AGM you have to place the switch on Spiral AGM to get the correct reading. If you leave it on Flooded, the reading will be incorrect because of the method each type of battery is tested. I wouldn't worry about the battery.
 
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