How to properly charge lead-acid batteries in series?
Oct 26, 2007 by Ubi | Posted in Engineering
If each of the batteries has the same capacity, then yes, you may connect them in series and use the (nominal) 48 volt charger. (it should have an unloaded voltage of about 55.)
The matter of unequal voltages etc, mentioned in a previous post, refers to every cell in a battery. There's nothing you can do about this unless you have access to the individual cell's terminals. And if you did, it entails a lot of buggering about to correct the problem.
Just make sure that each battery is discharged to the same point before charging them in series.
The state of charge is evaluated from the specific gravity of the electrolyte. Around 1120 for a fully discharged cell, around 1220 for a fully charged one.
If you want to be pedantic, search the manufacturer's web sites for variations with, and compensation for, temperature.
dmb06851 | Oct 26, 2007
Yes, you can charge them in series at 48. And yes, if they are not all in the same condition, then one may overcharge and another undercharge.
Better answer: why not charge all 4 in parallel on a regular 12 volt charger, if the charger will handle 4 times the current of one battery?
Parallel means connect all the positive leads together and put them to the charger positive terminal. And all the negatives together to the negative terminal. Then you can combine big ones, little ones, live ones, dead ones, etc.
Roy C | Oct 26, 2007
It probably would be better to charge each battery by itself , but it is not necessary . Golf cart batteries connected in series are charged that way on a daily basis with no ill effects. As the batteries charge their internal resistance is lowered. Of course the internal resistance of a battery never reaches zero even when fully charged.
Mr. Un-couth | Oct 26, 2007
Where is the electricity in lead acid batteries?
Nov 27, 2008 by Drunk and violent | Posted in Engineering
The source of the electricity is chemical energy stored on the surface of the battery plates (one lead, one lead dioxide). The conversion and transmission medium is a strong sulfuric acid (H2SO4) electrolyte in which the plates are immersed.
The lead plate combines with SO4 (sulfate) to create PbSO4 (lead sulfate), plus one electron.
(Pb) + (HSO4−) → (PbSO4) + (H+) + (2e−)
Hydrogen ions and SO4 ions, plus electrons from the Lead plate, create PbSO4 and water on the surface of the Lead Dioxide plate.
(PbO2) + (3H+) +(HSO4−)+ (2e−)→ (PbSO4) + (2H2O)
The tendency toward the above reactions is what creates the electric potential at the battery terminals. Connecting a load across the terminals permits a closed path for electron flow which permits the reactions to actually occur, and the battery to supply electricity and "discharge."
As the battery discharges, both plates build up PbSO4 and water builds up in the acid as the concentration of H2SO4 is reduced.
Providing a reverse voltage source across the battery terminals greater than the chemical potential difference reverses the chemical reactions, "recharging" the battery.
The electrolyte does not store energy, but conductivity of high molecular compounds is lower (logrithmically) with lower sulfuric acid concentration. Testing the specific gravity of the electrolyte is the normal way of determining state of battery charge.
Specific Gravity - Percent of Charge
1.265 = 100% for fully charged, (acid concentration about 33%)
1.225 = 75%
1.155 = 25%
1.120 = Discharged
Sulfuric acid is a strong acid with respect to its first proton
H2SO4 → (H+) + (HSO4−)
so even at low concentrations there will be some production of electricity while there are significant Lead-PbO2-PbSO4 differential areas.
Exchanging the electrolytes completely one time should still permit the originally charged battery to function (with much reduced performance due to much higher internal impedance). The exchange will not bring the dead battery back to life, although it will help any residual lead-PbSO4 differential provide some energy because of lower internal resistance.
I'd be interested in the result of your experiment, e.g. will either or both batteries now start your car? (btw, exposure of the battery plates to air will increase sulfation, a major cause of battery failure, so be careful and be quick.)
(Edited @8:40 am to give more complete physical explanation and alert about avoiding sulfation)
Bert K | Nov 27, 2008
Imagine switching out the lead-acid 
A hybrid that's more about style than the environment gasoline-electrics to use advanced 
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