Batteries again

Despite having replaced all three batteries last year, at the weekend the service battery was playing up.... To start with, I wasn't sure that it was the service battery, and wondered about other causes, but when I connected back to shore power, all was OK again.... I then sat down and thought about it for a while.... Its an 85Ah battery, and is now running an awful lot of additional stuff that it wasn't originaly specced for.... including typically a fridge and radar... so that in combination with things like an anchore light overnight have seen it off.... I reckon an average weekends consumption is probably something like 60Ah, which is too much for an 85Ah battery on a regular basis..... It didn't help that I accidently flattened it completely in the middle of last season... So I've decided to upgrade the battery bank.... Out with the 85Ah, and in with 2 x 100Ah deep cycle carbon plate batteries... both Elecsol.... I'll parallel them and then will have much more capacity, plus still have the failover battery for when needed... and the engine battery completely seperately... At the moment, due to lack of long cables, the fridge is directly connected to the service battery bank. I need to fix that, so that I can run the fridge off the spare battery if neccessary... another winter job!... it is possiblt to switch the spare over to the fridge in an emergency, by removing the leads from the regular service batteries and then switching to position 'both', but can't think of a reason why that would be an emergency right now!