You will wonder how you you could ever do without them when you get used to it.
I bought 3 of these 450 CCA jobbies a while back (2 for work 1 for me)
http://www.jaycar.com.au/lifepo4-12v...h-lcd/p/MB3762
Use 'em almost every day out in the field for power supply and they will turn over my 6.5 litre Chevy