[emeritus]

I have managed to dig out the copy of the SAFT Engineers' Handbook for Nickel-Cadmium batteries that I acquired at an exhibition in 1988 (30 years ago: time has flown!) and have scanned some relevant extracts relating to open cell batteries. Things had obviously moved on since the 1940's.

No longer recommended to change the electrolyte every couple of years, now only necessary to top up with fresh electrolyte if the S.G. gets too low. Topping-up with distilled water normally only required every 2 to 3 years if the specified charging regimes are followed, but may be needed every few months if the battery is worked hard. No mention of deterioration of electrolyte in the cell itself due to reaction with Carbon Dioxide: only the possible need to remove the thin layer of Potassium Carbonate that might form on the cell covers. Any possible fall in the specific gravity of the electrolyte is attributed to electrolyte having been carried away as a vapour when cells are gassing during charging. Possibly improved vent design now prevents ingress of CO2?

When putting into service after a long period of disuse, two cycles of charge and discharge (to 0V per cell) is recommended.

The efficiency (energy out to energy in) should be around 70%.