After prolonged simmering time in the head, the information I gained from this project finally clicked. I believe I have the solution for rejuvenating lead acid batteries. Brief testing appears to confirm this. Here are the relevant data forming the basis for the solution.
DATA 1
Many battery experts/enthusiasts on youtube stated their method for reviving a battery was repeatedly fully charging and discharging the battery.
DATA 2
I have a domestic battery charger, for AA cell's etc, that came with instructions on maximising the capacity by fully charging and discharging the cells.
DATA 3
I had personal experience of using a 21v-max 5W solar panel charging two different batteries on two different cars to 16v. The maximum theoretical limit for 12v lead acids is 16.2v. At 16.2v, the battery would have 0 sulfation and would be at the maximum capacity. The reason the batteries reached 16v was to do with the max charger voltage, and the charging and discharging cycle. During the day, the panel produced a nett surplus charge going into the battery. During the night, the car's sleep consumption discharged the battery.
DATA 4
What started this thread was the observation that a battery gained extra capacity after being charged directly by an 18v 200mA AD/DC power supply for a few weeks. The power supply only consumed 0.9w to 1.2w and didn't add any meaningful charge to the battery. But, a follow on charge using another charger with more power consumption produced the observed increased capacity.
The 18v power supply was feeding 80mA and drawing 20mA cyclically. The reason for that was the PSU faulting because it could not maintain 18v on the output - the battery dragged the voltage down to whatever the battery voltage was at. During the fault, the PSU drawn power from the battery. At the end of the fault, the PSU reset itself and started a new cycle.
THE SOLUTION
The common theme for each set of the DATA is that to affect the battery capacity, a cyclic pushing and pulling of current from the battery is necessary. The cycle period could be a couple of seconds in the case of DATA 4, or 24 hours in the case of DATA 3.
DATA 3 indicate that it isn't necessary to fully discharge the battery to eventually attain the maximum capacity. Although, it cannot be ruled out that full discharging would make the process quicker.
QUICK PROOF
1. The 063 (340cca spec) battery was charged to full at 250cca. This was confirmed to be a 'hard' limit from previous occasions
2. Charged 063 using the 18v faulting PSU for 1 day and obtained 252cca
3. Charged 063 using 32.5v 100mA for 1 day and obtained 253cca. The number would be higher after resting the battery.
The hard 250cca limit could not be surpassed no matter what I did previously. The pushing and pulling of the faulting PSU over came that. To recover more capacity, more cycles of pushing and pulling of current will be needed on the battery.
OBSERVATIONS
1. High voltage isn't the primary factor for recovering lost capacity. Although, to obtain 16v and max capacity on the battery, high voltage is needed. A conventional charger wouldn't be able to do that.
2. Pulse charging probably doesn't do anything, unless the pulse comprises positive and negative amperage parts.
3. Deep discharge of the battery results in semi-permanent lost of capacity that can only be recovered by the described solution. The mentioned 'hard' limit on the 063 is the result of deep discharge.
4. Injecting chemicals for battery revival will cause permanent lost of capacity. This was seen on my discarded 18 year old OEM battery.