iOS7

[zzm9980]

I've noticed the erratic battery life on my iPhone also. Maybe once every few days, the battery will plummet really quickly. I've mostly troubleshot it to errant applications in the background. Use the task manager to kill all of the apps, then shut down the iPhone/Pad and turn it back on. Seems to resolve it for me.

[nakatago]

Speaking of which, does anyone have any suggestions for apps to monitor data usage?

There's an ipad air (wifi only) here that I suspect gulps down data. The built-in usage utility only applies to cellular data.