I can tell mine b/c the other day I had the car off with the lights on to help a friend change a flat. Took no more than 20 minutes, went to start my car and nothing but clicking. Also, my cranking power has become less and less the colder it gets. I'm gonna wake up one morning and get no crank from my car. I guess I need to stop being cheap and just buy a new one already, 5 years/84k miles from a battery isn't too bad