The battery system was built around the existing (2 seasons old) house bank and internally-regulated 55-amp alternator. To this we added a dedicated cranking battery and a Xantrex Pathmaker battery combiner.

Power Needs

Compared to most cruising boats, our power needs are quite modest. We don't have many high-draw appliances aboard—no windlasses, watermakers, or refers. When we purchased the boat 3 years ago we needed new batteries, so at that time I calculated what I anticipated our power usage to be. I figured that in a worst case scenario—multi-day passagemaking with extensive use of the tiller pilot—we might use as much as 125 amp-hours of power in a day. But for the sort of coastal cruising we anticipated doing I couldn't realistically foresee using more than about 40 to maybe 50 amp-hours per day. And in actuality I expected our draw to be even less. Based on these numbers we decided to install 200 amp-hours of deep-cycle capacity. This wouldn't be sufficient for a full 24 hours worth of passagemaking demands—it is recommended to never draw your house bank below 50% of charge—but would provide us with sufficient power for a couple of days between charges while coastal cruising.

This worked well for the first two seasons, and we decided to stay with that for our house bank during the rewiring. However we also felt that it was prudent to have a dedicated cranking battery which is isolated from the house loads at all times. Our new system would be designed to include this, with the starting battery housed on the starboard side of the boat under the galley unit. Access to the space was limited so we ended up using a very small size cranking battery (Group 57, I think—8.5 inches x 7.5 inches x 12 inches; 520 CCA).

With the two separate, isolated banks and only a single output alternator, we still needed a way to charge all the batteries simultaneously. Ultimately we decided on a Xantrex Pathmaker battery combiner to fill this need. The Pathmaker is a simple solenoid devide which senses the voltage at the battery terminals and when it rises to a user-definable level automatically parallels the two banks for charging. When the voltage drops again (after the charging voltage drops or is turned off) it automatically separates them again. Additionally, the soleniod can be manually engaged for emergency starting purposes.