A set of 12 cells from long abandoned coach was set up on a 24v charger. None of the cells was split (luckily) and terminal corrosion was not too bad. These cells were thought to have lain for up to 5 years since their last charge. The cells were of the 4-post type.
Batteries were charged to maximum capacity, then discharged while being monitored. Cycle 1 yielded a capacity of just 8Ah. The s.g. of the acid in all the cells was measured and it was between 1.00 and 1.05 (at full charge). This showed that much of the Suphate in the acid had been deposited on the plates.
The cycle was repeated with the de-sulphator attached. This time 62Ah was recorded.
The cycle was repeated with the de-sulphator attached. This time 160Ah was recorded. At this stage, the discharge monitoring showed one cell suddenly going into reverse voltage, so the discharge was stopped. It transpired that one terminal of one cell had gone almost open circuit. Fortunately, the other terminal on the same plate was OK, so it was connected instead for the next cycle. Before discharge, the acid s.g. was measured and was seen to be in the 1.15 to 1.2 range. Desulphation was obviously working.
The charging was repeated with the de-sulphator attached. The initial charge rate was 8A for
about 10 hours, then the rate was reduced to about 1A while "the boss" went offshore for 2 weeks
to do the "day" job. On return, the batteries were checked and were giving a capacity of up to
300Ah, i.e. almost 'as new' capacity.
The batteries in this experiment were of 'middle' age. Some much older cells of type BRA1 have also been brought back to life. These cells have date stamps from 1974 to 1981, and it has been possible to raise the sg of the electrolyte from 1.0 (at the start) to 1.25 (after several weeks and cycles).