Many thanks for advice guys. I was sure it must be possible as I did it with a small motorbike battery and it worked.
My problem is that my boat has 15 6V LA batteries in 3 banks but it is left for many month unused. I don't really like leaving live batteries on her. Nor do I want to exhaust
them doing nothing.
I'd really like some cost effective batteries that I can use when I need them and not when I don't.
But is that really a practical possibility?
Problems are how to quickly and safely remove electrolyte; how to safely store it or dispose of it; where to get and store new battery acid; how to test the battery is OK one new acid is put in; where to buy good quality old style batteries that can be opened and drained or topped up as necessary.
I am thinking that maybe truckers might have some solutions to these sorts of issues.
Finally what about old style batteries and fumes? Such batteries must have been used on boats in years gone by and I am wondering how fumes were detected if present and how over charging
and gassing were controlled for.