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I could see on my scope that the voltage would shoot up above 12 volts maybe up to 17 volts or 20 volts, just for a very short duration. It was explained to me that these voltage spikes break down the crystals that have formed on the plates, but I did not carry out an experiment to investigate this claim since I'm not a chemist. You might want to explore this angle of the problem if you have the background.
3) maybe or maybe not, I'm sure there are differences between batteries. We are here talking about lead acid batteries only.
Those brief overvoltage pulses when applied to
the lead acid battery are capable of rejuvenating
it. In a battery which has lost capacity it is invariably
due to significant buildup of phase changed lead
sulfate (aged hardened crystals) which are resistant
to normal charging voltages.
The overvoltage pulses are effective in converting
the hardened sulfation back into active plate materials
while regenerating the sulfuric acid electrolyte. Once
successfully desulfated (reconditioned or rejuvenated)
the battery will again demonstrate full capacity providing
the plates haven't been damaged by abuse or by physical
shock.
The voltage on the lead acid battery is a good indicator
of the state of charge but ONLY following a 24 hour rest.
A sulfated battery will show a higher than normal voltage
while being charged, particularly with overvoltage pulses,
which creates the illusion of charging or increased energy
storage. Once the battery in this condition has rested for
24 hours its voltage will properly indicate its state of charge
as it will be less than the normal voltage for a fully charged
battery in good health.
Some heavily sulfated batteries will show a near normal
unloaded rest voltage but when load tested will have
little capacity and the voltage will decrease rapidly due
to excessive internal resistance caused by weak electrolyte
and considerable hard sulfation.
It is remarkably easy to rejuvenate and restore a "dead" lead
acid battery which hasn't suffered any internal damage with
a simple desulfator circuit.
For there is nothing hidden that will not be disclosed, and nothing concealed that will not be known or brought out into the open.