Why are batteries typically measured in miles, rather than years and or recharges? Age and charge cycles are the two hardest things on batteries, not distance traveled. I for example will not drive 500k in my life, but I'm sure the battery is going to have much less capacity and life left in 10 to 20 years regardless.
It depends on what you are talking about. If you are talking about a battery car, then it is better to use a number that makes sense for the end user, and number of charge cycle is not an easy one. If you recharge from 70% to 90% every day, is that a cycle, is that 1/5th of a cycle?
The main problem is the number of full capacity cycling a battery cell can do can change widely based in how it is used. So it depends on how it is integrated into a car and how the car is being used. A typical Li-Ion cell will last a few hundred cycles if cycled completely at a high rate without proper thermal control. But this number can easily be multiplied by 10 with proper thermal management, not charging it to max voltage and doing shallower cycling. If you want to give a number for a final product, you are bound to make assumptions on how it will be used. And at this point you just have an equivalence between distance driven and cycling count.
Also, age has less impact than cycling count in the context of a properly designed battery pack. The two main factors for battery degradation are time spent at high temperature and high state of charge, and cycling count (with speed and depth being the key elements). EV manufacturers are keeping a buffer for that purpose and their batteries do not spend a lot of time at high state of charge where the chemical degradation is more effective.
