A battery monitoring app like that would need to run as a background service. No way a developer can make one of these without going the jailbreak route. Perversely, an app that monitor's how much juice apps are using would also use more juice, though a well designed one might not use much.
There are apps that will give you some system info and estimate how much battery life is left for each type of activity. I use SystemInfo, but there are lots of them. Just search for system info or system monitor. Take everything they tell you with a grain of salt, and the understanding that what would be bad on a computer is probably just normal for a mobile device. Memory is often full, or nearly full as apps wait around in case they are needed. They are automatically freed up if memory is needed. Usually.
Once every month or two it is a good idea to let your iPad run until it automatically shuts down. Then put it on a charger and leave it there until you have a 100% charge. This isn't like memory for the old Ni-cads. Instead it is a way for the iPad to reset its stats for the battery, and provide more accurate estimates.