Long ago I read that sulfate left on battery plates eventually hardens.
In addition, it’s good to have a battery well charged before hitting
the starter because the surge can knock sulfate off the plates,
shortening battery life.
I’ve been putting a charger on my car battery if it gets down to 12.55 V
or less. I take it off when the current tapers to a certain point. A
few days ago, I checked to voltage 8 hours after taking the charger off.
It was 12.78. It must be a Maintenance Free battery!
Because the cell covers appeared to be removable, I assumed it was Low
Maintenance (Sb/Ca) and not Maintenance Free (Ca/Ca). The two are
charged differently. Nowhere on the case does it say what kind it is.
Online, manufacturers of lead/acid batteries no longer seem to say which
model is which. (Nowadays, Maintenance Free batteries often have
On the farm, cars used to have Low Maintenance. I used a Standard
battery (Sb/Sb) in the truck because they were supposed to stand up
better to vibration. I used a Maintenance Free with cushioning for the
tractor because a Standard battery can self-discharge at 2% a day in hot
weather. The tractor could sit for weeks and be far from an outlet.
I’d charge any battery if I found the voltage down. The automatic
charger had a switch for Maintenance Free.
Somewhere, I got hold of the Battery Council International’s 1978
Battery Service Manual. It devotes 6 pages to Maintenance Free
batteries. A graph of “typical charge voltage characteristics” shows a
Standard battery being topped off at 14.6 volts and a Maintenance Free
battery at 15.7 volts.
My car’s regulator delivers 14.4 volts at normal temperatures. If it
were set higher, it would be bad for a Low Maintenance or Standard
battery. That explains why I need a charger to top my battery off. The
Service Manual says Maintenance Free batteries charge on a taper. That
explains why it takes hours to bring it up a little to 100%.
The charger I use now, has 2-millisecond pulses. It doesn’t say so on
the case, but I checked it with an oscilloscope. It seems that the
microprocessor determines the spacing of the pulses according to the
voltage between pulses. Apparently, this allows it to charge any kind
of car battery without a “Maintenance Free” switch.