I installed the build
rockbox5gb20080117.z ip advertised in the "Viewports Sim..." thread and ran the battery benchmark I can't remember now whether the volume was set to -25dB or -30dB.
I left it running until the battery died, which was at time 06:47:38!
The previous battery test on my 5GB H10 ran for barely 4.5 hours, so this is almost 50% better.
Très bien!