Redarc, an Australian company, has developed a very versatile portable power system - Goblock:
For over a year I have been using the 50Ah model (0.6kWh) for camping. It can be charged from domestic (eg 240V AC), solar (direct connection up to 30V, inbuilt controller) or a car (7A trickle charge from 12V socket or direct connect to start battery when engine is running - auto cut-off when not).
It is expensive but it has been very useful, particularly when the skies are overcast.
Being lithium batteries I am guessing that it would be difficult to get them delivered overseas but it is good to know the technology is out there.