iPhone 5 battery goes from 20% to 1% in less than 10 minutes

Recently been noticing that my battery "bottoms out" quickly once I hit the 20% remaining level. I've done full reset, forced discharge, the works. But it will routinely drop normally down to 20% (I'll get the alert) and then in a matter of 10 minutes or less, drop quickly down to 1%. In some cases, it will go straight from 16% down to 1%. And then it will auto-power-off.

Doesn't matter what I'm using it for. Will happen while I watch it, phone doing nothing other than screen glowing.

Other than trip to Genius bar....any other ideas?

 

I went to the Genius bar, confirmed as bad battery. They replaced it.

Also, kill FaceBook app when not in use.....sucker eats battery like crazy.