Question about portable car battery jumpers

Star2236 thought this was worth mentioning said

I have one like the ones they sell here on meh, that you plug into the wall to charge and then hook up to your car battery to jump. In the little info booklet it says not to store in extreme cold or hot heat and in Michigan your car outside can kinda get to both. So my question is do you store the potable battery jumper in your car year round?
My car was completely dead twice yesterday and I didn’t have it with me (bc it’s summer in MI and inside a car can get really hot) both times was a pain in the ass to get jumped. So really what’s the point of the battery jumper if you can’t carry it in your car for cases of emergency?