My iPhone 6 has started to lose it's battery charge very quickly. I will be charging the phone, and when I unplug it, it will drop to a different percent. It will die at random charges, and comes back to life at a lower charge. Advice is appreciated.

Here you can find some useful tips on how to make the battery life of your device longer. They work for both iOS 8.2 and iOS 8.3.

https://www.apple.com/batteries/maximizing-performance/

http://www.idigitaltimes.com/ios-82-battery-life-problems-how-fix-quick-drain-is sues-iphone-ipad-and-ipod-422229

Try to reset your device. This won't delete your data stored on the phone.

• Press and hold the Sleep/Wake button
• Press and hold on the Home button
• Keep holding both buttons until the display turns off and back on with Apple logo on it.

Alternatively, you may go to Settings - General - Reset - Reset All Settings

https://support.apple.com/en-us/HT201559

If this does not help, restore your device to factory settings. Note that this will erase the data from your device.

Take a look this Apple Support article: Use iTunes to restore your iPhone, iPad, or iPod to factory settings - Apple Support.

If you battery drains extremely quickly, you need to visit your local Genius bar and ask for diagnostics/replacement.

Hope this helps!