Note These packs come discharged. You must charge them according to manufacturers instructions (probably 3 hours) before using as they aren’t factory charged Kind of cruel but true. Maybe that makes for safer transport from factory to store.
With modern cars, I have shied away from giving or getting jump starts. The underhood area of a modern car is very limited, meaning if a jumper cable slips off, it could get tangled and damage the engine or start a fire or fry one or both alternators. In the past few years, the lithium battery based “safe” automotive boosters have become more appealing.
One of the popular models available from AutoZone at the same price as Amazon is the Noco GB70 for $200. Realize that the specifications given prominently on the case are a bit exaggerated as typical for automotive products.
This unit does seem worthwhile and safer than using plain jumper cables. I have not evaluated it in very cold weather, noting that all batteries lose substantial ampacity as temperatures lower.
Lithium vs. lead-acid automotive jumper packs
Lithium batteries are less than 1/4 the weight of a similar capacity lead-acid battery, as the inexpensive jumper packs use. My priority was size and weight, so that I could take the pack with me on field experiments and day trips. Thus I paid twice as much for the lithium battery pack so that it doesn’t just sit on the shelf as a complete waste like the heavier lead-acid pack would.
Lithium battery charger specs
The Noco models below claim a 3-hour recharge time. They come with a cigarette lighter charger, that recharges the pack in 3 hours. This cord is reversible into a jack, that will power many 12 V accessories for some time (based on the Watt-hour or Amp-hour rating).
I would not try to power AC inverters off the lithium battery packs above, the capacity is too small. You would more likely want a plain 40-80 Amp-hour or more lead-acid (AGM) battery to power AC inverters.
Notice that you can charge cell phone batteries several times off these jumper packs.
Although I can’t verify the information in the videos, their commentary may be informative.