ultra small jumper battery
 

This seems like a handy device for the rear shelf cubby. Will charge your phone if you're stranded late at night.

$on sale for 80 at the link below.
(Amazon has it for $105)

Cobra® JumPack™ Ultra-Compact Portable Charger & LED Flashlight w/ Jumper Cables ShopHQ.com

jump a car with a 7.5 amp battery????

There are guys on Amazon jump starting SUV's with this thing. I was thinking it would be handy if the battery dies and you can't get the automatic trunk release open to access the car's battery. Maybe with a cigarette to ubs adapter it can feed just enough juice to unlock the trunk?

i have a similar one .... not the same brand.... works great & like a charm. can jump start a weak battery immediately ... or in another case, totally flat battery (wouldnt even turn the starter) ... i left it attached for 15 mins before cranking (also attached) ... and the engine started no problem!

highly recommend having one (a high quality and safe one, with inline fuse) for emergencies. i bought it initially ... to be able to go out rescue any stranded family member .... ended up using it more myself :D