battery dies after big sur update

I have a 2013 macbook air. I have a nearly new apple battery with only 120 cycles. Before I upgraded to Big Sur it took a full charge, the design capacity was 100% and I got 9-10h of battery life. I upgraded to Big Sur and IMMEDIATELY my machine told me the battery needed replacing. Also the design capacity had dropped to 80%. With each successive charge the battery design capacity dropped by about 5%. Also, the battery would run down to about 30% very quickly and then drop to 7% to 2% in the blink of an eye and die. I ran through all the diagnostics, did the SMC and PRAM resets etc but nothing worked. I finally uninstalled Big Sur and downgraded to Mojave. My battery however is still wrecked. According to coconut battery my mac OS battery status is GOOD and sitting at 130 cycles. Full charge capacity however is only 1549mAh instead of 7150 mAh and the design capacity is sitting at a lowly 21%. I'm I'm lucky I get 70min os use now on my battery. Thanks BIG SUR! Does anyone have any REAL solutions to this issue. Please don't offer me any of the 'excuses' that Apple has in terms of letting the battery drain fully and recharging it or the SMC reset stuff. None of it works. Please also don't suggest that it's a coincidence that my battery is wrecked after installing BS because it's not. This is a 6 month old Apple battery that was noticeably problematic immediately after installing BS. Thanks in advance for your advice.