How do I replace clock battery
clock battery may be weak, sometimes resulting in hard starts. battery hasn't been replaced for at least 5 years.
I have yet to see one of these batteries fail. To test it, have an ethernet internet connection, go under the Apple in the upper left hand corner to System Preferences, Date and Time, set it to automatically sync with Apple. Look to see that it has done so, now uncheck it. Shut down and unplug the machine and ethernet overnight. Now plug it in and boot up. Check the time. If it is OK then your battery is fine. If not let us know to get directions on how to change it.