I'm looking for a battery to replace the one in my Landis& Gyr C/H
controller, model RWB200; I thought it didn't have battery backup, but when
I took it off the wall there was this totally dead battery in it.

The controller is otherwise fine, and does all I want it to, so I'd like to
replace the battery, but I can't find any reference to it.

The cells are about 15mm diameter and 6mm thick, and in this case have been
heat shrunk and soldered (or something) together in series. I have seen
some in an old Maplin catalogue - single mercury equivalent cells; VQ76H -
that look right, but theyre not rechargeable.

I've no info on the controller - it predates me here, but it's a 2 channel
24hr 2times per day digital and seems pretty up to date.

Anyone any ideas on batteries that might do, please? I can't seem to find
anything close - RS have Varta button cells (can't give you the link, it's
one of their time expiring searches) which look vaguely right, but are
nowhere near the size.

TIA

mike