Unlikely. Battery is not linear enough to extrapolate to 1% or so and 5% means 20 steps, which, for 10 hour uptime at least means "average consumption over the last 30 minutes or so" which is pretty much useless.

Also, consumption in such a device is anything BUT linear. In reality, the screen eats depending on what was displayed (not backlight), GSM actually works via fast bursts, disk works async as flushed, CPU drains ROUGHLY with load, since different tasks that ceil the CPU drain differently - that's why there are testing-benchmark algorithms instead of loops. Wifi works in bursts, headphones eat with volume and signal, etc.

The only linear drain in the N900 is most likely the backlight.

This one of the reasons we use Li-Po in phones, they deal well with spikes. Unless one has an accurate, fast, hardware amp-meter, it doesn't work.

Estimated uptime left on mobile PCs is easier to detect because the drain is bigger in standby, because there are amp-meters built in in some of them and because miniature drains like bluetooth don't really count when you drain 150W with the CPU and 150W with the GPU.

If you try on N900, the variations in usage (popping the screen, changing songs) will throw your estimation off by hours, which is worse than just watching the battery IMO.