mountainsoft
Thinks s/he gets paid by the post
I love those, and I've used it once. Many of them also have USB outputs so you can recharge your phone when camping or wherever.
I used mine a few times with my old car. I didn't drive it much so the battery went dead fairly often. The battery sure beats jumper cables, especially when no one else is around.
I bought jump start batteries for my wife and daughter's cars too, but I don't think they've ever had to use them. I try to recharge them every 6-12 months or so to ensure they're ready to use when we need them.