Chosen Solution
I purchased iPhone 6 plus battery on ifixit.com. I replaced it, but it died after the first charge,I think so. The device doesn’t turn on at all. The old genuine battery works well, I think I got a bad battery from ifixit.
Do you have access to a multimeter? If you do, then you could measure the actual battery voltage. Anything above 3.2V should allow the phone to boot. If the voltage is lower and it doesn’t take a charge, then you may have a defective battery. In that case, contact iFixit support.
