I drove to the dealer and had the battery in my car checked. It failed the "load" test, so I bought a new battery. Now, I can use the car without worry that I'll get stuck somewhere.
When I was young, cars had an amp meter instead of a volt meter, and you could see the battery condition by the amount of current being drawn. A lot of current was drawn to start the car, but within a few seconds the current was down to a low level due to the battery being recharged. Now, with modern cars, I don't know how to tell the battery condition. Yesterday, my battery allowed the radio and parking lights to work fine, because those items used low current, but the battery didn't give enough current to start the car.
I was reading about testing car batteries, but the procedure was complicated and something not a lot of people can do. What is needed is a simple procedure that doesn't require anything that doesn't come with the car. People need something that is part of the car and shows the battery condition. The driver thus can glance at the meter and know the condition of the battery.