411 Celebration Service Battery size - help!

Hi,
Can anybody confirm the size of the batteries supplied as standard on the 411 Celebration? Reason being, mine have pretty much had it, yacht is in Spain (I am not!). I quickly measured them as:
length 50.5cm
width 18.7cm
height 20cm. Terminals both at the one end.
The originals (x2) are Tudor (seem to have been discontinued ... typical!) and a neat,tight fit in a customized tray under the Starboard rear bed. I quickly measured them as thought they must be a standard size and would easily identify replacements back in the UK. Trawling the web, the measurements I took seem anything but standard and I am questioning my sanity/state of inebriation when I took the measurements.
Can anybody help? Even better, recommend decent AGM/GEL replacements?
Kind Regards.. John.