I have seen several friends use those jump packs...
My only question is;
...Will they still work after being ignored and bouncing around unused in a trunk for 8 years. I usually see a minimum of 8 years of life from a (often used) starting battery and replace them before a non-start issue; batteries will usually tell an aware person that they are getting weak.
...jumper cables work when needed (usually to help others, including field welding)... pack and ignore.
Enjoy!
No. One of mine loses 10% every six months, one loses 20%. You should charge them twice a year, but you could probably get away with once. For an expedition rig, you could just plug it into a 12v source (wired or using the included car charger) for constant charge. That way eight years would be easy.
Oh, and you shouldn't let stuff bounce around in your trunk. And jump boxes work when you're alone, which seems like a better feature than "emergency welding."