>Over 24 hours, the voltage value I've been displaying (rounded to the nearest tenth of a volt) went from 4.2V to 4.1V. So even under the most unfavourable roun

>Over 24 hours, the voltage value I've been displaying (rounded to the nearest tenth of a volt) went from 4.2V to 4.1V. So even under the most unfavourable rounding that's 0.1V over 24h, or still about 95% battery charge. That would be almost 20 days doing some basic processing, screen updating, etc every minute. How're you calculating that? Voltage of (what I assume is) a lithium ion cell is a pretty poor way to measure state of charge - the discharge curve maintains voltage pretty well until 80% capacity before falling off precipitously. You certainly aren't going to get any work out of the cell below 3V or so without risking permanent damage.