So I have an IPhone 7 plus almost 3.5 years old phone and its 295mAh battery is almost dead though it shows 80% battery health remaining but I think its rather only 20% and apple is coding it to prevent it from going below 80 as it'll block peak battery performance.
So coming to the point, I have a bricked iPhone 7 and 6s Plus in my box. I opened them both and found iPhone 6s plus battery is actually bigger than 7plus battery, so I tool battery out of iPhone 7, which is way too smaller. I glued some double sided tape near to battery so that it won't move.
Finally I clicked the start button and guess what, It was drained out so I threw it over the charger for an hour and half.
Clicked On button and my phone came back to life. No bootloop, no lag, no glitch.
Battery health in app menu shows 97% battery health and I have tried playing games over this new battery and a 30minute Pubg Mobile takes about 8-9% battery, So I could now play approx 10games with full charge.