I don't have that spec macbook but having replaced the battery in a couple different machines at this point... your number aligns with normal wear and tear. And honestly, even at 80% it isn't that bad. It's bad when it starts dropping out during regular use where it'll drop from 100% right down to 80, and lower and lower... then you might want to get a new battery or figure out what you want to do. ~3-5 years is about the lifetime of lithium batteries.