Like how does this happen? let's say you own your iPhone for 2.5 years and saved up to at least 300 cycles of charge used and now your battery's capacity is at 80%. How do you experience this? does the iPhone goes from 100% steadily to 20% and then it automatically shuts off at 20% while the battery bar shows it still has 20% left? or does it rapidly go from 100% to 80% very fast and then goes steadily from 80% to 0% slowly then shuts off? If you have any first hand account or have any information of this, plz tell me. Thx!