Someone who is less lazy than me still should work out the math... what would the TOTAL power consumption of the device be over 100 years?
Because I don't think you can get around the power issue unless you use nuclear materials (might be hard to source now that Ghaddafi is gone) or go with the mechanically stored power.
Anything else - heat, light, batteries or whatever else will always require human interaction, and I think the fact that it will run for 100 years untouched is the appeal of the device.
If the total amount of power needed was known, the mass and height of a weight could be calculated needed to power the device. Plus, it would be pretty cool that, year-after-year, the weight drops fractionally... like a few millimeters or less. Almost like... "when the weight reaches the bottom... you're dead"