Adding a Starting Battery…
The attachments describe a change from 2 batteries
(Group27 + Starter battery) to house bank of 2 grp27 plus one starting battery. The change was made to our Mark 2
(1990), with minimal cost for materials.
In addition to the G27 and existing starter battery in the battery box under the Starboard Settee, I had an extra deep cycle G27, from a previous boat. Without getting into inverters, isolators, -combiners, etc, I just wanted to add “ampacity” to the house bank, and keep the starter battery topped off for turning over the motor.
Wiring the 2 deep cycle batteries in parallel makes it
appear as a single big battery with twice the amps. The ‘1-both-2-off’ switch on the panel works as before;
charger has its own leads, so charging at the dock will charge both banks (all 3
batteries). I choose to locate the starter under the aft quarter berth. I figured the wire length (voltage drop)
would be no worse than the current configuration. I only had to add the ground cable (#2 welding cable from the
electrical supply store; they crimped on the ends) from the starter battery to
the engine block, and the platform to hold the battery.
The platform is plywood, coated in epoxy. It has 3 legs made from bolts from the
hardware store. Once I had the
platform level, I mixed up some epoxy and glued the bolt heads to the hull. I already had the battery box, and I
bought the battery strap from WM. Last summer I was working for GE
Transportation Systems, so I couldn’t swing a cat without hitting an
electrical engineer. Several
engineers sprinkled the plan (diagrams) with holy water, so I had high
confidence. After one season, it works. Now
on the hard, I took some pictures (which match, but don’t look like, the
diagram). Any questions, you can contact me.