Hello
I've been using my BV8000 Pro for about 3 months. Its battery usually lasted for 1,5-2 days. But about a week ago or so it began to perform strange. The battery life lowered to less than one day, while no more applications were installed and I haven't changed the way I use a phone through a day.
I suggest battery capacity decreased to 50% of initial value. I used advanced USB charge tester (J7-4T) when charged the turned off phone and it showed only about 2000mAh from full discharge to 100% charged state.
Can you explain why this could happen and how to fix this?

If a factory reset doesn't fix your problem, your battery is faulty. In this case please contact your seller to get a replacement under warranty.