Quoting Roger Ford: Quoting Myles: No, it's not lead-acid.
What is it then? I'd be most surprised if it wasn't. It might have the acid in the form of a gel, or absorbed in fibreglass, but the basic technology is almost certainly lead/acid. This page has a link to the Varley technical sheet which describes them as lead-acid.
Absorbed glass mat batteries from Wikipedia. (The acid isn't absorbed into the glass fibres, it just likes to keep the mats wet.)
Gel batteries from Wikipedia.
Jonathan
Edited by - Jonathan Kay on 14 Jun 2014 07:59:14