Why, yes as a matter of fact it is quite possible for you to replace the battery in your phone yourself. As a matter of fact, that's the whole premise behind this entire website!
You'll need a minimum of tools to do this job; a small Phillips screwdriver, an opening pick and a plastic prying tool are really all that's needed for your phone; iFixit's iOpener toolkit would be a great place to start.
[product|IF145-198|iOpener: iPhone and iPad Screen Opener, Adhesive Softener|new_window=true]
Unfortunately, iFixit isn't omnipotent and cannot possibly make guides for every possible device out there in the world (although they're giving it a really good try!), so they don't have one for your phone. However, there is a Spanish site that has just what you're looking for; a guide to replacing your battery.
Hi @n3kliiy2jsqagy,
Why, yes as a matter of fact it is quite possible for you to replace the battery in your phone yourself. As a matter of fact, that's the whole premise behind this entire website!
You'll need a minimum of tools to do this job; a small Phillips screwdriver, an opening pick and a plastic prying tool are really all that's needed for your phone; iFixit's iOpener toolkit would be a great place to start.
[product|IF145-198|iOpener: iPhone and iPad Screen Opener, Adhesive Softener|new_window=true]
Unfortunately, iFixit isn't omnipotent and cannot possibly make guides for every possible device out there in the world (although they're giving it a really good try!), so they don't have one for your phone. However, there is a Spanish site that has just what you're looking for; a guide to replacing your battery.
[link|https://www.nadiemellamagallina.com/en/manuales/smartphones-1/xiaomi-191/xiaomi-redmi-9-1289/bater-a-11487|Manuales / Xiaomi Redmi 9 / Drums|new_window=true]
That should get you going! If you have any questions, fee free to ask.