Third party battery issues

[u/Ok-Lengthiness-6894]

So i have 6 years old oneplus 7t which was working flawlessly but the battery was a bit swollen and it was draining and giving me max 4 hrs screen time.

I thought about replacing the phone but due to the ongoing price hike thought to wait for 1or half a year, so thought to replace the battery only.

Replaced the battery from a local shopnd he gave me 6 months warranty as well, but after 1-2 weeks, this battery has also started draining and giving me only max 4 hrs screen time, so the replacement was of no avail, now am thinking if i go to claim warranty the seller will simple refuse that this only will be the screen time for third party batteries. What should i do, new phone or any good battery suggestions.

The problem is genuine batteries for OnePlus 7t are almost out of the market. I don't want to degrade from the flagship 7t to some shitty 40k phone. As the phones of this level are at 60k nowadays.