i fly at a club field with a bunch of other pilots. my powerlab 6 charger with powersupply can be plugged into a generator or home outlet. i fly batteries in series and parrallel so for me it's easyer to charge a # of batts for saturday and sunday with 9+ flights possible. but rarely do i fly all the batts and still get plenty of air time.
thing is i don't mind buying extra batteries to be ready,but for those who want to save a few bucks they should buy a charger to plug into their car.[of coarse gas costs too]
skip the car jumper idea as it dosn't hold that great a power, and deep cycle batts work but weigh a ton.