Locate and wire them together
Not only should they be located close together, but all advice I have received and discussed says they should be combined as one battery bank. This includes all of the benefits of having twice the battery power and is simpler and more reliable. The problem with wiring two batteries in parallel to double the amp-hours and keep them at 12 VDC is that the two batteries MUST be the same age and style and brand. They have to be as identical as reasonably possible or else one will emerge as the stronger of the species and wreak havoc on the other one. The charging levels will be determined by the strong one and the lesser/older one will never get fully charged, then begin to suck off the other one.... The short of it is that adding a second battery to the boat is the right opporunity to buy two new batteries at once, and then to replace them together 3 or 4 years on, and so on. Little Diana, which is a first-generation H-25 not unlike the H-27 inside, has two size-24 batteries under the after end of the settee berths, which is perfect for weight distribution. It's enough for about 3 full days on full battery power. I made the battery compartments using cheap WM-brand plastic battery boxes; they open with lift-out plywood panels (in fact, following nearly identically the Cherubini 44 practice!). They are wired together with 4-gauge wre passing under the floor and connected to a Blue Sea off/on battery switch mounted in the front panel of the quarter-berth. From there the electrical system and the rest of the boat thinks there is only one battery. I NEVER switch from one to the other-- that's only asking for trouble. JC
