Replace the battery, trust me. I had the same issue and kept using it until the backcover started to click open. My battery was bulging at this point and whenever I was using the phone it would heat up and drain dramatically, the bulging movement it made at that point clicked the backcover open. New battery took me 15mins to replace and now my dad is using it without issues. You should've seen the battery when I took it out, you could see that it had been bulging because the wrapper was totally creased and the battery was rippled.
Edit: My phone would heat up, the battery would drain and charging it in the car or with a powerbank would not prevent the drain. Only stopping everything, laying it down and charging it with the wallplug could charge it back to 100% 
Second edit: First, backup everything, remove data and cache and install your ROM fresh. If that doesn't help, just invest in a new battery they are fairly cheap and iFixit has a decent guide on how to replace them in about 15mins
Last edited: Jan 14, 2018
Pra nav and Rusty NZ like this.
