Fast battery drain after having it replaced... twice

So a week ago I noticed my phone’s battery got swollen so I got it replaced.

Thing is, the new battery drained fast and the battery indicator didn’t work right. It stayed at 100% for a couple of hours of usage before going down as it should be. Furthermore, there were big drops in battery percentage, like from 50% to 10%. The huge drops often happened when I stop using my phone for about an hour. The drop is sudden, like it’s a vertical line in the battery usage graph.

I went to the repair shop again and had it replaced AGAIN and same thing happened. The battery is stuck at 100% for hours before working properly. I was once charging my phone but I had to go outside. It was at 50% charge while charging but when I unplugged it, it suddenly became 100%.

I suspect it’s either battery calibration or the replacement batteries don’t actually have 3750 mAh capacity (Honor 8x design capacity). I installed Accubattery and it initially diagnosed that the battery capacity is 1000 mAh. Furthermore, based on real time stats, it indicated that it used around 1100 mAh to go from 100% to 0%.

Any thoughts or solutions?

Things I’ve done:

• Factory Reset
• Battery “Calibration” - Drain the battery enough that I literally couldn’t turn it. Charge it to 100% and leave it plugged an extra hour, while the phone is off. Turn it on again and drain it to zero again before finally charging it to 100%.