The jump packs I own are essentially a case, cables and some accessories wrapped around an AGM golf cart battery. The two times I’ve done the replacement the battery was significantly less expensive — about $30 vs about $70 the jump pack cost originally. Unfortunately my favorite jump pack (The “Powerstation PSX” and later models, sold by Costco, no affiliation) doesn’t seem to be manufactured any more, so it’s worth it to me to buy a new battery every few years to keep the two I have operational. When charged after every use and also once a month I get about five years of service out of them.

I’ve seen a number of jump packs that are pocket sized or nearly so, based on Lithium Ion battery technology, but I don’t own one. I do not believe that they have enough cold cranking amps for reliable winter service.