A very rough estimate for phone batteries is that they last 1000 recharge cycles. If on average you recharge every day, that's 300+ charges a year, and there you go, an expected life of 3 years. That phone is up for a battery replacement. Just like oil or wheels need to be replaced in a car.

Now, how many charges does a car battery do, and how frequently it tends to need one? The same calculation from phones can indeed be translated to cars, the only mistake is translating the end results of the calculation. Maybe that helps with your father?