I have recently changed the battery for my s21 ultra. The price for my s21 ultra battery was Rs 2500 incl gst, and labor cost was around Rs 550. I think for your s21 plus it will be moreover the same. You can also check in service centre once.
Well I feel battery backup has slightly increased sometimes I get good sometimes average it all depends on usuage nowadays there's lot of network fluctuations from 5G to 4G because of this battery is consuming more in some locations. Overall it depends on usuage. If your battery is gone better get it replaced soon.
