My iPhone 5s is stuck on 8% while on the charger... please help?

This is like the 4th time my iPhone needed to be taken to the iPhone repair shop. After about 1.5 years of having my iPhone 5s, it began to stop charging & I would wake up to it being completely dead & not being able to turn on or charge, while on the charger. The repair guy says that it's my motherboard, and there's nothing he can do about that. But what he does is gets my phone to charge & turn on when I bring it to him. This time I brought it to him, he turned it on & got it to charge so like yeah. On my way home I looked down & it when from like 100% to 8%, and I was like ***??? So I hurried home, put it on the charger, and ever since its been stuck on 8% on the charger, and it's been 3 days. I have never dropped my phone or got it wet in any way.

I want to unplug the charger & let it die so maybe when I replug the charger it'll turn on & charger regularly, but I'm afraid it won't turn back on when I plug the charger back in. What should I do?