After 2 years, I decided to replace the battery of my phone (XIAOMI MI-9) with this one. I thought I bought a battery with the same characteristics as the factory one, however, from the first week, the phone doesn't last a whole day with moderate use. I can say that the factory battery, after 2 years of use and hundreds of charges, had better performance than this new one!!!

What I can confidently say is that it does not support the basic features of the manufacturer, such as fast charging. Dimensionally, it is narrower than the one it replaced. Also, the nominal battery capacity is 3300mAh, but its actual capacity does not exceed 2400mAh, measured with accubattery, but this is also evident in its usage (it may drain even faster than the one it replaced)...
Furthermore, through accubattery, the health of the original replaced battery had reached 75%. The new one, so far with about 15 charging cycles, has not surpassed this percentage.
Another problem is that it does not support the fast charge of the charger...
In conclusion, the worst €15 I have ever spent!! And because some will jump in and say "come on, it's only €15," I write all the above not to complain about the €15 obviously, but to protect the next ones as much as I can...

I bought the battery because it said "Bulk" and indeed, when it arrived in my hands, it seems to be a Bulk Xiaomi battery for the Mi9. It was in the familiar white cardboard packaging that Xiaomi usually uses, and the battery itself was sealed in anti-static nylon. It appears to be authentic. Time will tell.

Edit no1
In less than 4 months, the battery - phone, where it had, for example, 70%, the device would tell me that it was experiencing "battery depletion" and would shut off. I waited a bit, and when I pressed the power button, the device turned back on, showing that it had battery. Occasionally, it would continue to function normally, or it would shut off unexpectedly.

In simple terms, the battery became useless after approximately 4 months of use. It was replaced with another one from a different store, and the device is working perfectly again for about a month now, with significantly improved battery life compared to the previous battery, which I was not satisfied with even when it was new.

In simple terms: It's a waste of my money and a hassle for me to wait for a new battery to be delivered and go through the trouble of installing it again.

Well guys, you should be careful where you buy your batteries and what I mean by that. Pay attention to the stores where you buy the batteries. I bought this particular battery from a well-known store and within 2 days it swelled, resulting in my phone shutting down at 70%. So, I had to buy another battery from a different store, which is genuine without any issues. Do your research before buying a battery and ask for a warranty.

I changed my first mobile phone, it had reached 2000mAh in 5 months. I read on the internet that generally, new ones have 2700-2800mAh instead of the advertised amount. Indeed, I tested it after changing to a new one and it is 2800mAh. In other mobile phones I had, like Xiaomi, the battery was as stated. It is unjustifiable for their flagship to have such a poor battery.