Why is my iPhone black but will only vibrate on configuration

[sconrad123456]

Hey. Yesterday my boyfriends iPhone 5c went black. We thought it was dead. But won't charge and turn on.
The only thing we can get it to do is vibrate short once when we press the lock, home and both volume buttons at once.
It doesn't vibrate when plugged in or with the sound switch.
We think the battery died last night as it wouldn't vibrate this morning but after charging for an hour it does again. Still no screen lit up. What's going on?!?

 

[Ledsteplin]

The 5c needs a new battery. It's not holding enough charge to function properly. My old iPhone 5 does similar. I charge it several hours, but all it does is show the battery icon on the lock screen.