I bought a Porta-Jump MAX from Repco a few years ago to get me out of trouble on remote area camping trips but never actually used it so it's been sitting untouched for at least three years. It claims a five year shelf life. Anyway my girlfriend's car got caught with a flat battery the other day so I gave it a shot before using the normal jumper leads. I used it direct to the battery rather than through the cigarette lighter and it worked a treat. (I un-characteristically followed the instruction to the letter). The MAX is the bigger unit recommended for 4x4's and boats. It wont fix a defective battery, but I reckon it's well worth having on board to get yourself out of trouble, particularly for longer trips away. It only weighs about a kilo and doesn't take up much room. I'd be keen to hear what success others may have had. Regards, John