A major life-limiting problem with lead-acid batteries is that when discharged (partially or otherwise) the resulting lead-sulfate slowly transforms into an insoluble form that eventually disables the battery. (A charged battery is shown, where no lead-sulfate is present.)
In this instructable a novel (resistive) pulsing approach is described for driving the lead-sulfate back into solution that is faster than the more traditional inductive method.
Sulfation is not the only aging mode in lead acid batteries, so while desulfation may extend the life, it will not do so indefinitely. Last car battery I had lasted 8 years, but after that time it was internally distorted, and desulfation would not extend its life further.
Step 1: The Dilemma
Attached are pictures of the reversible spongy form of lead-sulfate, and irreversible crystalline form.
Various methods of driving the insoluble lead-sulfate back into solution have been proposed and tried, all based on over-voltage. One rather intrusive method is to replace the sulfuric acid electrolyte with a greatly weakened version and then apply an over-voltage for a prolonged period of time before restoring a full strength electrolyte. A less intrusive approach is to use inductive voltage pulses, but this is speed limited since the inductor needs to 'charge up' and this takes time. The idea of pulsing is to allow recombination of hydrogen and oxygen between pulses.
A less satisfactory approach involves EDTA chelation where the lead-sulfate is chemically removed from the plates but not returned to the electrolyte.
Step 2: A Counter-intuitive (resistive) Approach
An alternative approach is resistive based and was discovered accidently (by the author), and is still not totally understood. It was found that if a resistive load is applied and then released, a high over-voltage pulse results at the battery terminals and an oscilloscope plot is attached showing a more than 15V over-voltage pulse (which is above and beyond the 12V of the battery).
As well as being simpler and cheaper than an inductive approach, it can run up to 1000 times faster.
Of course that still leaves a mystery (I love mysteries) as to why the battery kicks back in this manner.