My phone will no turn on, can someone please help me?

I have an iPhone 5 and my power button has never worked because it is a second hand phone it has never really bothered me until now. I have started to have problems with my battery and it keeps dying on 50% etc now it has got to the point where it will not turn on i have had it on charge all day and the only thing that shows is the low battery sign. it will not turn on what so ever. i have tried loads of methods to try an turn it on and i haven't been so lucky. it is a huge disadvantage seen as though my power button does not work.

has anyone got any ideas? It will be much appreciated.