Another point: dead battery completely tanks permance and makes macbook unusable. Could only turn on with charger. Had some 10+ years old macbook - cpu was thro

Another point: dead battery completely tanks permance and makes macbook unusable. Could only turn on with charger. Had some 10+ years old macbook - cpu was throttled to some 500+ mhz (with charger attached) After changing battery, computer flies again.