Hello, I noticed this battery packs here: 3800mAh battery for DJI Mini 2 For DJI Mini2 battery| | - AliExpress
They claim that thery have more mAh (more flight time), but is it real and how much it's usable ? Will the drone detect it properly and work properly with it ?

These batteries seem alright, however I do not like to buy batteries from other sources that are not DJI directly. Because non-original batteries can void warranty, straight up not work, or even worse, cause a fire/explosion. If you check LiPo fire on the internet, you will see, it is pretty serious stuff!

These batteries seem similar to the ones sold by DJI Androsean, a YouTuber from Kazakhstan who also sells extended flight time batteries for different drones, including Mini 2.
HOWEVER, he warned his users to not update the firmware on their drones because DJI is blocking such batteries to be used, so if the drone detects a non-original battery, it will not start the motors.
I would link to his video, but his video is in russian.

Thank you for the reply.

I am not worried at all about warranty, I only want the battery to work.

What do you mean by fire ? To overheat during charging ?

I literally got my Mini 2 last week and never wanted to update it, for a specific reason.
It came with 01.03.0601 and it is currently still with it.

I don't know if it will work on my drone, but I found DJI Androsean's channel and Telegram channels and asked a person there about this, let's see if and what he will reply...

Hi, Infinite FREEMAN. Thank you for reaching out. The Intelligent Flight Battery of Mini 2 only has 1 variation which has 2250 mAh. For safety purposes, we encourage everyone to purchase the original battery from our website or authorized dealers only. You may check this link to see the nearest dealer in your place: https://www.dji.com/where-to-buy/retail-stores. Thank you for your kind understanding.