AT AMAZON, a sale on jumpstarters and power supplies. I had occasion to use mine recently — the dome light in the Mazda had been left on for about a week while we were out of town — and it worked perfectly. Much easier than calling AAA. It’s the first time I’ve used it to start a car, though I’ve used the built-in air compressor a number of times. (I have this model, which is now discontinued; it’s been fine but I’m sure the others are just as good — when I bought it, it was because it was cheap, not because I did extensive research.)