[williamstein]

These "jump boxes" are amazing! I used to keep big jumper cables and have AAA in case of a dead battery. Last time AAA came (after I waited hours...), they just pulled out a little "jump box" and instantly started my car. I found and bought a random one on Amazon (there are dozens -- https://www.amazon.com/s?k=car+jumpstart). It's very small, can also be used to charge a cell phone, as a flashlight, etc., and really works. Every ICE should have one of these in the trunk.

[pdkl95]

Note that the battery in a "jump box" is probably capable of discharging a dangerous amounts of energy at very high current. BigClive measured[1] over >500A when he tried to discharge one of these batteries, which didn't actually work. The internal Li plates probably separated, breaking the circuit before fully discharging. After starting to disassemble the battery and realizing the that the plates had separated he attached a voltmeter and measured a full 3.6V across the supposedly-discharged, partially disassembled battery (squeezing the battery with his hands, "This still is fully charged, but it's just puffed up... that's a bit scary." Later, after the Li plates start changing color (!) - probably metallic Li starting to rapidly oxidize - they spontaneously ignited (pyrophoric).

The benefits of having a spare "jump box" in the trunk are obvious, but it's important to remember that this means carrying a dangerous amount of energy in form that is a very serious fire risk if anything damaged the battery.

[1] https://www.youtube.com/watch?v=0tGK1nqXr28