I received it with 3.8V and after installation, the mobile phone returned to levels of performance of a new battery.

Genuine Xiaomi battery for Mi9 and Mi9SE is of the correct thickness and has the adhesive strips integrated on the back, just like the original one. It does not come with an installation toolkit. For those who shop from Chinese sellers, be careful as there are many imitations circulating that even local merchants cannot always detect the differences. It is good to communicate with them before making the purchase, as I did, and they responded promptly and flawlessly. It does not heat up more than the factory battery during charging and has the correct duration of usage and charging, just like when the phone was purchased new 3.5 years ago.