When I use a 2 GB SD card with my C6, I gotabout 52 minutes of continuous video recording at the highest quality setting (I don't know if this made the camera work harder because of high data bitrate, thereby using more power).
To get over 50 minutes of battery life, I just hold the camera and let it record, without using other power-hungry functions like the optical zoom. The autofocus will consume some power, but the scenes were far enough away itprobably did notrefocusvery often. I don't think you can switch off the LCD when you are recording (closing the LCD may put the whole camera on standby, not only stopping the recording!). In essence, I can't think of any way to improve the battery life.
I bought a non-proprietary (non-Sanyo) replacement battery pack but it has the same power rating as the original Sanyo pack. I know nothing about rigging up my own extended battery pack.