What is the best 12 volt battery jumper for emergency jumps. You know these battery packs that you can carry in the trunk. Do they work and what are the do's and dont's with them? Are they worth it. I see ones advertised on QVC many times. How long do they last? Thanks. Like to hear your experiences. I have a 93 blazer I keep in the garage and the battery at times dies because I forget to run it often enough. Now that I have been retired for awhile I just do not use that truck alot. But do not want to get rid of it. It is the backup vehicle. When it happens I have to get the pickup and then use 2 sets of jumper cables to reach the front of the blazer and is a pain.