Lithium Batteries have limited Shelf Life from Date of Manufacture, even unused. The _original_ Li Battery on my backup-to-the-backup Powerbook G4 just died after ~8 years, even though it was plugged in to the Charger 99% of the time.
Note that I was only getting two years out of the Lead-Acid batteries in my old Powerbook 100, and when those Batteries died, they had a nasty tendency of taking out the fuse on the Motherboard. So things have improved.
Or ~850 hours out of a 100 watt Solar Panel= ~110 days, assuming good conversion efficiencies and ~8 hours of Sunlight a day. Say three months in reality to recharge, assuming no other Electrical load.
That's the energy content of ~2 Gallons of Diesel Fuel...
and by now some wheels should be spinning...
Diesel Fuel Cells!
Diesel-Powered Fuel Cell Produces Clean Electricity - IEEE Spectrum
(Generating Diesel Fuel on the run is difficult, unless one does a fair amount of deep-fat frying with vegetable oils.)
The _only_ reason that Electric Cars on the road, like the Tesla, makes sense now is that the Charging Infrastructure mostly already exists. (Formula E is making inroads in off-road Motorsports, and I think that it's really cool. Still, only a handful of Tracks are equipped so far.)
Such Infrastructure does _not_ exist for Sailboats, and it is very unlikely, given the diminishing market, that it ever will.