Thanks for the replies. Attached is a picture of the Ni-Cad battery and you can see the differences in level especially the second cell from the left is much higher that the others. My concern was how it got to be this high level.
The right most one may have a leak as I can't see any electrolyte in it? I think I will have to take it apart to see. This may be awhile before it makes it to the top of the to-do list. Fortunately I have some spare cells from the original build back in the 1980s!
It may be of interest to know that this was the standby lighting battery in my vintage OB van and has come to attention because we plan to restore the van to it's original condition see the partially written website.
www.mcr21.org.uk
When It comes to charging I do have a clever "PAG" multi function charger that claims to restore batteries, we'll see.