That is all a jump pack is an easy to carry battery with cables. We've had a spare battery mounted on a cart for years at the home shop. I have that SO jump pack at work and like it. When I bought mine, it was with in dollars of any other pro grade jump pack I priced.Do jump packs do anything that a spare charged battery in the trunk with jumper cables won't do? Besides be a little lighter. Just asking.
Can make your own jumper box and it is cheaper to do than buying a store bought one.Have one at work using a 300 cold cranking amp riding lawn mower battery and heavy duty jumper cable leads.Just secure the jumper cable leads somehow and hook it up to a battery tendor when not in use.I have seen car batteries used too with jumper cables hooked to the car battery too.