As I do my own iPhone battery replacements. Couple of pointers for you, if you don't want to go to Apple.
1. Contact tonyvision .in see if they have battery for your model, if not just buy from amazon or any other place. Don't pay more than 2k.
2. Once you have your 3rd party battery, don't worry about how it looks or what's written on it, go to any mobile shop preferably small one where you can see the guy working on your phone, ask him if he can remove the original battery without damaging it in any way, if he says "yes" only then tell him to install this 3rd party battery but don't glue it in yet, just close the phone and get your original battery with you, don't leave it at the shop.
3. At home charge it all the way and keep it on charge for 2 more hours after it reaches 100%. Let it deplete to 0% until the phone switches off, then charge it again to 100% without disconnecting. This will do the battery calibration.
4. Now use the phone like you normally do and see if it performs okay, gets you the backup you need, if satisfied then go the shop get it properly glued down with adhesive tape. If in case you don't feel any difference in performance, just get it removed put original battery back in and process the battery return.
The thing is if you glue it down with adhesive tape initially and then you try to remove the battery, most of the time adhesive tape breaks in the middle of removal and then you have to get the battery out with a pry tool which damages the battery. In that case you won't be able to return the battery. Side note - The removal of original battery the very first time can be done by an expert without damaging it, because it is placed by apple with very high tolerances and pressure which is predictable and aids in removing it cleanly just by pulling the adhesive tape tabs carefully.
Don't give the mobile shop guy more than 500 cause all he is doing is replacing the battery that you brought.
If you feel like the guy is genuine let him source the battery and do all the talk about "I will test first then I will pay" cause testing process will take 2 to 3 days.
In all cases keep the original battery with you it will help you to sell the phone in future, because with third party battery you will get non-original message, don't worry about it, it's harmless doesn't affect any functionality of the phone, it is just a pop up notice that goes away.
Some Extra Info regarding this.
The original iPhone battery has BMS in it, which can be removed and put onto the 3rd party battery, this will fool the phone into thinking that your 3rd party battery is original. This process involves carefully opening both the battery to swap the BMS. Don't do it and don't let anyone do it for you.
Some info regarding third party batteries
Most of the time they are bad if not bought from good source. Even the good ones sometimes not work exactly like the original, but they are good enough and can last as long as your original one did. For example you might see things like battery runs great from 100% to 20% but after that it just starts dropping really fast. But it doesn't matter at that point because even in that state the third party battery performs so much better than the original worn out one. It really gives it a new life.
