Or you could do what the modern manufacturers have done, reduce the electrical load. LED lights and modern ignition that only charges the coils for the time required for saturation.
I agree, even if I still use an old RITA with 4 volt coils, I've run a LED headlamp for years and the battery stays charged even with a lot of low speed work. In the old days I used to fit a 3 phase, but unless you plan to use accessories like heated grips etc. there's really no need.