I want to keep this simple so as not to tax the patience of my fellow Sailnetters. I currently have (2) group 27's on board. I have a battery selector switch and an on board (West marine) battery charger. Am I correct to assume I have 2 group 27 banks (1 battery each)? When I put the selector switch to BOTH, I'm using them both as if they were (1) bank?
I was considdering adding another battery and putting the (2) existing ones together as one bank, maybe keep the other for dedicated starting? I know the options are many. I really don't want to get too complicated.
To DIRECTLY answer your questions; you currently have 2 banks. each bank is comprised of a single group 27 (90 AH) battery. When you put the selector to BOTH, you are combining the two banks into a single (180 AH) bank, which has a 90 usable
You *could* connect the two batteries together into a single bank, but if one of them has been used differently than the other, then they will have different charge "profiles." By combining the two, you will get the worst attributes of both of the batteries. It is USUALLY
preferred to create a single new bank from (in this case) two new, fresh, identical batteries.
I would not do this unless I was sure that the two batteries had been treated similarly.
I am currently in the same boat as you, so to speak. I have two group 29 batteries (105 AH each). I have been careful to treat them both the same in terms of charging, and discharging. I plug in to shore power, and keep them at 100% SOC.
This year I may build a platform, and buy another battery box to store them and a third (group 24 starting) battery on. This will give me a 100 AH usable capacity, and a dedicated start battery.