Can't fully recharge my iPad mini

It very well could be an issue of meter calibration rather thn the battery itself:

1. Allow the iPad battery to run down as close to empty as practical, then recharge fully.
2. Try a reset: Simultaneously hold down the Home and On buttons until the device shuts down. Ignore the off slider if it appears. Once shut down is complete, if it doesn't restart on it own, turn the device back on using the On button. In some cases it also helps to double click the Home button and close all apps from the tray before doing the reset.
3. If the above doesn't help, you may need to take it in to an Apple store for a look (make an appointment), or contact Apple service to see about an exchange.