Batteries with longer life?

I would like to buy batteries with longer life than the ones that are standard with the hpx250 camera.

When I used the 100B, the batteries, that look just the same, lasted about 5 hours. On the 250, these things seem to go 45 mins or so.

I know there is more in this camera, but the tape drive must have been a big power hog.

I've searched the Panasonic sites (and others, of course) to no avail. Anyone using a longer-life battery with the P2 cameras?

Regards,