When it comes to high tech, downsizing is often looked at as a sign of progress. Microprocessors meant whole computers, for the first time, could fit on a desktop. LCD displays made them portable - in the form of laptops. Moore's law proved that chips that once would have been classified as capable of enterprise-level computing now occupy devices that easily fit in your pocket. And advanced lithium-ion batteries meant you could finally take yourself off the AC teat for an appreciable amount of time, and you could charge your gadgets over and over without worrying about the ridiculous cycling fatigue that plagued earlier rechargeable systems.
If you're a rooted user, chances are that you flash new ROMs fairly often. What you may not know, however, is that your phone saves the battery statistics from old ROMs, and if you've never recalibrated your battery before, then your time away from the charger may not be as good as it could be.
Resetting battery stats can be an intimidating task for those who don't spend a lot of time in recovery (or who have never even booted into recovery).