they make these portable jump starters in many different sizes for different demands - there are the smaller ones like MADDMOE linked that are great for 4 & 6 cylinder engines and they go all the way up to ones like this one - NOCO 2000 Amp jump starter that are good for 8 liter gasoline and 6 liter diesel engines.
I had a DBPower jumpstarter that I carried in my slingshot until last year - like DJohnson had happen it started swelling up. after doing some research I found out that it was a common problem with that brand if they were stored over 90 degrees which around these parts is almost every day - after doing more research and hearing all good things I decided to replace it with one from NOCO - this is the one I now carry - NOCO Boost 500 Amp jump starter - easily big enough for my slingshot and probably any car I might be asked to help
I had that Boost 500 and it didnt work for me i got fed up with it and tossed it for the one i have now, they probably all Chinese made.....