I checked and it looks like the PowerPC's were power efficient. The 667Mhz model usually ran around 14W up to a maximum of 19W. The G5 processors were known to be hot and needed a lot of power. I remember having a PowerBook with a G4 back then, and remember closing the lid without shutting it down, and coming back days later with only a few percent's of battery draw. Of course, performance wise, the Intel mobile CPU's at the time were starting to really pull ahead of the mobile PowerPC chips at the point, except for a few very specific workloads.