A handy find by folks at Cult of Mac that can give you a good idea of all that is running on your iPhone in the background is an app called Activity Monitor Touch which is basically a tiny port of the Mac version. The app displays tables and graphs for your device’s performance stats such as processor, memory usage, battery level and uptime as well as a list of running processes. You can even setup an alert by tapping the alarm icon besides the battery which goes off the moment your battery is fully charged.
Testing the app, the source notes:
One fun trick is to quit some background apps while viewing the memory usage page – you’ll see the used memory bar shrinking down as you tap wiggling app icons in the running-apps tray at the bottom of the screen. (To get to it, double-tap your device’s home button, then tap-and-hold on any of the icons you see.)
Unlike the desktop app, this doesn’t let you meddle with running apps directly. You can’t quit processes from the list of what’s running.
Here’s the official iTunes desctiotion:
? Just like Activity Monitor on your Mac, AMT is the most handy and pretty system monitor app in the App Store!
? 4 in 1 app: Battery Status, Usage Monitoring, Device Information, and Process Monitoring
? Increase battery life by ensuring full-charge with sound alert
? Beautiful, useful, and universal. Buy it once and use it on your iPhone, iPod Touch, and iPad!
– Supported models: iPhone original / 3G / 3Gs / 4, iPod Touch 1 / 2 / 3 / 4, iPad WiFi / 3G, iPad 2
– Overview page showing device UDID, capacity, free memory, battery power, and network state.
– Detailed usage information on memory. View free space and realtime CPU activity.
– Battery state and remaining time for standby, gaming, surfing the net over WIFI / 3G, audio / video playback, and reading books.
– Alert message & sound when battery is fully charged.
– Active process list.