I looked into this long ago - started a thread - way back though. Since most gear converts AC to DC internally, I always wished I could just use the DC from the batteries to directly power the gear - get rid of the sine wave altogether. I'm not sure if that is possible, as you'd have to seriously step up the DC to high voltage. Some gear (Redwine, Teres Turntable, Sutherland PhD, etc) is designed to run off DC directly. I would certainly pursue this. I wonder if some manufacturers might be willing to accomodate a "special" version that could be switchable b/t AC and DC input. One manufacturer who might be amenable, as he is interested in the technology, would be Ralph from Atmosphere. Maybe you could get one of his amps and preamps made for DC - and be quite happy with that. I think it's a good idea to have a dedicated set of batteries for your hifi, so "sag" from other parts of the system doesn't effect your sound - but I don't know enough about it. I do know that when I was looking, the choice of inverter seemed to be an important question. The inverter makes the sinusoidal waveform, and you want a pure sine wave form - and you want to know how well the inverter can handle short peaks in power demand.
What region of the world is your island in? I'm in the Pacific NW (USA).