In reality, a lot of drivers say that their car still has more than 80% of its original capacity after 200,000 miles. They tend to have a flatter voltage curve, which makes it hard for the computer to judge their state unless they reach the top now and then. The combination that wears out the most is a full battery parked in the scorching sun. If you have to fully charge the car, timing it so it doesn't remain at that level for days is an easy and practical precaution. The number on the screen is important, but so is the temperature.