Right...update.
Went to boat yesterday,all batteries completely flat,tried to jump but wouldn't,put on charge,digital reading was 3.6 ,left on charge for hours and not really much improvement,think starter battery is flat so bought home to try and charge.had a marina engineer who was passing look at it ,said the big elecsol 220 battery is for the inverter and needs a lot of charge.left boat with no 12 v,even radio went off.he said I need a 240v charger so when plugged into shore will charge the batteries...so frustrating.any help very much appreciated.might be something silly...hopefully