Re: How big of a starting battery do I really need?
Even the smallest car starring battery you can find will start that motor. With three group 27's as house there will never be a need to use the "starting battery" unless you are not practicing good battery management. At 50% DOD your house bank will still have gobs more cranking capacity than a single group 27 at 100% SOC... You might even look into some of the motorcycle or small tractor batteries.
A group 26 auto battery is about the smallest you'll find. You may also do okay with a U1 lawn and garden battery if you buy the highest CCA or MCA version you can find.... Some of them have CCA's (0F) of 350 and at 32F at 400CA. This means that at 70F you'll be well over 450 cranking amps..
There are also the Odyssey AGM's such as the PC925 or PC545. These are small batteries. I install a fair amount of the PC925 and they have a 380CCA.
I have one that has been starring a 3YM now, as a dedicated starting battery, not just reserve, for about three years. They take near identical charge voltages as the flooded batts so no charging issues there.
-Maine Sail / CS-36T
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