The life of your MacBook Air’s battery is measured in cycles, which is the amount of time it takes for the battery to go from 100% to 0%. Depending on how you use your MacBook Air, going through one cycle can take a few days.
It’s important that you don’t confuse battery cycle with charge cycle, as they are two different things. One full charge does not mean one cycle. If you charge your MacBook Air’s battery 10 times, that doesn’t automatically mean it also went through 10 cycles.