Suddenly black screen on boot up

Hi hope u r doing great i hav macbook air 2019 model 512/16 FYIM i hav only used 12 gb from it I power it off when i am done using it and also keep it charged properly but recently i hav seen whenever my laptop is below 50 percent and i bootup it logs in to user and suddenly screen turns black i press the power button and it shows low battery even theres still 50 percent power so whenever i plug yhe charger in it than shows the current battery and everything works normal no shuting down afterwards my mac used to work like charm and i charge it properly dk what has happened i have than the smc reset and beleive me after the reset when i logged in same thing happened again any solutions? Should i stop powering it off more often and leave it on sleep mode awaiting for u ppl to help thnxs