iphone 6 won't charge

i was recently given a iPhone 6 and was told it was broken. they also said if I could fix it I could have it, so being me I checked to see what was wrong with it. it wouldn't charge. i don't know the last time this phone had been charged, so I attempted to charge it. nothing.I tried multiple cords and bricks. i then proceeded to check the internet for any answers. some websites said to check the lightning port for lint so I made sure nothing was in the port. and still nothing after hours and hours of charging. I'm assuming the battery is dead, but I want to ask if any one has solved this problem without taking it for repairs, and how?