Effective Power is a viewer for Apple's power logging diagnostics in PLSQL format. As the name suggests, these files are SQLite databases with a wealth of power-related information spread across many tables. Effective Power is my attempt at making sense of some of this data and presenting it in a useful way. The usual disclaimers apply: the files this tool works with have been reverse-engineered, so take a grain of salt when interpreting its results.
iOS internally stores energy metrics as PLSQL files. If you have a jailbroken device, you can pull them directly off the filesystem. If your device is not jailbroken, the easiest way to pull these files is to take a sysdiagnose, extract it, then look in the logs/powerlogs folder.
Alternatively, you can follow Apple's instructions to enable battery life logging, which involve installing a debugging profile.
The profile will be valid for 7 days, and will create day-by-day logs as you use your device. Once you have enough data, sync with your computer and the PLSQL files will be copied over, compressed, and placed in ~/Library/Logs/CrashReporter/MobileDevice/.
Once you decompress them, you can load them into Effective Power for analysis.