[quote=Deputy Dog]

[quote=jigsaw]

That is no problem with a lead-acid battery powered jump starter because that battery can be charged with the alternator in the car without danger of overcharging.
That way it is no problem to use it all day long, just leave it connected for a few minutes when the engine is running, and you will get enough power for the next jump start.
Do not try this with a lithium-ion jump starter, it could be very dangerous (you will hear a warning sound if it is connected when the engine is on).