With everything else going on in my life over the last year, I ended up neglecting my batteries. They got VERY low on electrolyte. topped them up but age and neglect meant that at full charge they were only reaching 12.45v.
So they had to be changed only they were 2x US Battery L16HC a 6v monster with 435 amp hours weighing 54 kg.
Wasn't able to get US battery replacement as they were a couple of months on the wait list, but was able to get very quick (48 hour delivery) of Trojan L16H - a direct replacement, although they were not actually in stock at the warehouse.
Congratulations to Tayna.co.uk for your quick service and good prices.
Very many thanks to staff at Port Solent who assisted me to remove the old and add the new batteries.