If you're only gonna word process, read, or do light office duties the G74 will do fine with a 75W limit. I have an 100W inverter that we run in the car during long drives across big ol' Canada, and my G74 has never tripped the overload protection on it (it can do 80W continuous,120W peak). But I don't game or do anything else heavy duty while on it (I recalculate spreadsheets alot but that only takes a few seconds each time, and the inverter can handle intermittent peak loads).
G74SX-CST1-CBIL, i7 2630QM 2GHz
32GB DDR3 RAM @1333MHz
GTX560M 3GB DDR5 (192 bit)
17.3" LED 1920x1080
Sentelic TP, BIOS 203
Debian Linux Wheezy (Testing) Kernel 3.2, NVIDIA 295.40