MacBook Air Battery: Full charge capacity is 1/3 of Design Capacity

Hello Folks,

TL;DR: Full charge capacity is 1/3rd of the design capacity but battery health still shows as good (480 charge cycles). Downgrading to macOS Mojave changed a few things but did not fix the issue.

Detail: I have a Macbook Air (2013 Model). I got my battery replaced a little over a year back. I earlier had macOS Big Sur but I started facing battery issues on that. The issue involved battery percentage dropping from 90% to 7% which basically made working without a power source quite difficult. When I checked in the battery settings - the battery health showed as "Service Now". I read on some forums that downgrading to macOS Mojave could help in such a case so I tried doing that.

Once I downgraded to Mojave, few things changed. The battery health is now showing as good. However if I open Coconut Battery (Image attached), the full charge capacity is almost 1/3rd of the design capacity. It has completed 485 charge cycles which is not much and should not pose this issue. Surprisingly, the battery health is showing as good. The battery while charging jumps from 27% to 100%. While discharging it goes to ~80% and drops to 4-5%.

I don't think I can avail warranty any more cuz it is a month or so beyond the one year and the store has not been receptive. I was wondering if this is an issue which could be potentially S/W related since things changed when I downgraded my OS.

Please help. Thanks!