Having done more research, I could order one of these from a caravan dealer 25 miles away now. The EFOY 1600 (that's 1600 watthours) costs a trifling £3479! The 10 litre methanol cartridge costs £34.99 (342 pence per KWatt Hour!).
The good news is that it weighs only 7.6 Kg. I didn't ask the price of the smaller EFOY 600 (which would be more useful for an ebike, perhaps) because I was mainly interested in the possibility of replacing my off-grid Lead batteries. Still some of you rich guys might want it instead of the A123s