How to measure battery health?

It appears "there's an app for that." Check this out....... http://itunes.apple.com/us/app/battery-go!-plus-battery-management/id388530619?m t=8

I was prepared to say that the app recommended above wouldn't do the job but after looking .... maybe it will, in the way it approaches things, but I don't think you really need it.

The only way to really know the state of your battery's health is through how it performs in normal use, which is the only spec that is provided by Apple. The test you go through is a multi-stage one, as follows:

1. Run your battery all the way down, in normal use, all the way until the iPad shuts itself down.
2. Now re-calibrate your battery metering by plugging it into a known good charging source, for which read the Power Adapter which came with it, and charge it all the way up to 100%. It will take a few minutes before you see and hear your iPad come back to life.
3. Once it reaches 100%, leave it overnight. The next day, just use it like you normally do, do whatever it is that you normally do; but keep on doing it until the battery goes flat and shuts it down agaion. Make note of how long this took. The average user should expect about ten hours of use out if it, on wifi, less on cellular, depending on how heavy your video loadng is.

The recalibrating needs to be done every month or so to ensure that the metering (the percentage that you read) remains fairly accurate. If you fail to do that, eventually it will no longer be.

If you get less time before it shuts down, try it again. If you consistently get much less time than you should, then you definitely have a battery capacity issue and need to start talking to Apple.