The battery inside these units are long lasting and you’ll easy reach 4+ years life span.
Battery life is normally around 500 full cycles (full charge and run flat), but that means there is still 70% battery capacity left. If less than full cycles, then more partial cycles are possible.
If (say) you do a cycle from 100% charge to 50% charge, this is half a cycle.
So you can expect to do 1000 “half cycles”.
Of course, temperature is also a factor.
