Hi nifeman, thanks for your interest.
Sadly, not much success to report on my end.
I have found a 36 volt golf cart charger for my 20 cell array with fresh electrolyte. It only pushes 15 to 20 amps into the array. At this point, I have charged this array 3 times, but have not gotten the voltage to rise above 33 volts. Individually, all cells show a 1.3 to 1.4 voltage when at rest. I have no reason to think that any individual cell is preventing the array from achieving the desired 1.85 volts per cell on forming charge (or 37 volts for the array).
It leaves me to question if this constant current charger is pushing enough amperage to overcome the internal resistance of the cells. The other possibility I feel most likely is that the cell plates have become saturated with carbonate particles, and that the cells need to be reconditioned before their voltage will rise to the specified forming charge level.
My next step is to rewire my test load. Since I was previously using a 12 volt array, I had wired the DC bulbs into parallel. Now that I have a nominally 24 volt array, I need to rewire it into a series-parallel configuration so I don't drive the bulbs with too much voltage. Once I do so, I can run some proper charge-discharge tests on the array to see if it improves in final charged voltage and/or amp-hours discharged (I will arbitrarily stop discharge tests at 1volt per cell, or 20 volts for the array).
Thanks to AZsun for the thoughts on creating the single cell charger, and other info. I have looked into the welder builds you described. I think I can replicate this, and am on the lookout for an old microwave to salvage the transformer from.
Since I have a charger that does ~6 volts with enough amperage, I may stick with that and try to recondition 3 cells at a time. My biggest obstacle is figuring out how to heat the electrolyte and pour it. I agree with AZsun that this is a delicate and dangerous process and should be done carefully and thoughtfully.
I am busy with summer projects at this point, and will report back after the weather has turned and I have more time to proceed with the cells.
Thanks to all for the continued interest, and as always feedback, thoughts and constructive criticisms are welcomed.
Thanks.