This is the simplest and most convenient way we've seen to provide 12V power anywhere, anytime. The Baintech PowerTop is basically a 100Ah Gel battery with a box of bits screwed to the top. Yes – there is no box around the battery which means it takes up less space! All of the goodies – including a solar charger, DC-DC charger, and even a 240V charger are built into the top module – along with 3x Anderson plug inputs and 3x 12V outputs – including cigarette lighter socket and Engel posi-fit sockets.
Best prices we can find online are here – Baintech PowerTop 100Ah Battery Pack.