I got an Antigravity Micro-Start Mini (XP-5) last year, since the Lexus seems to love flattening it's battery, and I now need to use it everyday as my main transport. Of course, now I use it everyday it no longer flattens it's battery so I haven't needed it 0 even a couple weeks ago when I parked up and went to a gig, came back 4 hours later to find I'd left the interior light on, the battery was still fine!

However, it's an awesome little bit of kit - barely bigger than a smart phone (bit thicker) but will jump a V6 engine multiple times in a row no problem. Mine's a straight six (2L) and I tested it by disconnecting the battery completely, connecting the jumper cables to the battery cables and turned it over - instant start, no fuss.

You've just got to remember to keep on top if it's charge. It will naturally discharge itself, especially when left outside in a cold vehicle over winter. You shouldn't really try jumping things if the batter is below 75% and not at all if under 50%.