IPad Air 2 shuts down at 50% power

For a few weeks my iPad Air 2 has been shutting down when it gets to 50% power. The low battery signal comes on and I have to plug in and wait for it to come back on. When it does it is at 50 - 56% and then charges all the way to 100%. I have shut down as much background stuff as possible and do a reboot each time. What else can I do to stop this from happening?