I have seen those, but never considered it. Why driving around with
> heavy stuff on the miniscule chance that you will ever need it? And
> also need to top up the battery in the pack. I'd rather swap the car
> battery as soon as any hint of trouble. (Saab 9000 235,000 miles)
You keep it at home. Mostly, a car will fail to start in the morning. And not every car has a flat battery because the battery is faulty.
Mine gets used mostly for tyre inflation. And as an easily portable 12 volt supply.