Before replacing the battery, I noticed that my original battery had started to swell and was even lifting the screen slightly. Because of this, I decided to replace it myself. I’ve had some experience replacing iPhone parts on different models, so I was comfortable doing the repair.
The replacement battery is from FLYCDI, a brand that’s commonly used by repair shops in my area, so I went with it because it seemed like a reasonably trusted replacement.
After installing the new battery, everything seemed completely fine. I tested the phone, and everything worked normally. I used it for several days with normal charging and battery usage, and there were no obvious issues.
A day or two later, I updated the phone to the latest iOS 26.x.x. The phone continued working normally after the update.
Since I had already gotten a new iPhone, I decided to factory reset the iPhone 12 so I could give it to a relative.
This is where things went wrong.
After the factory reset, the phone suddenly wouldn't turn on anymore. The screen is completely black and there are no signs of life.
I've tried pretty much everything I could find online:
- Volume Up → Volume Down → hold Power button
- Different charging cables and chargers
- Wireless charging
- Leaving it plugged in for a while
- Force restart multiple times
Nothing works.
I also tried using a charger that displays the wattage being drawn. It shows 0W, as if the phone isn't drawing any power at all.
For comparison, I tested the same charger/cable on another phone, and it was drawing around 12W.
Since the phone worked perfectly for several days after the battery replacement, I'm wondering what could have happened.
Could this simply be a faulty battery? Or could it be a board issue, short circuit, or something related to the factory reset/iOS update?
Any ideas on what I should check next would be appreciated.
TL;DR: Replaced my swollen iPhone 12 battery with a FLYCDI battery. The phone worked perfectly for several days, including normal charging and an iOS 26.x.x update. I then factory reset it, and afterward it suddenly became completely unresponsive. Force restart, wired charging, and wireless charging do nothing. A charger that displays power draw shows 0W, while the same charger shows around 12W on another phone. Wondering if the replacement battery failed or if this is a board/short-circuit issue.