Battery is coin-type  CR2032 lithium.  Shelf life of 3-5 years.  Recommended replacement after 2 years for remote installations.

To change battery, pry black backing off with knife blade, this is only cosmetic.

Set clock, then set timer.  Then turn to Manual OFF then back to Auto.  Timer will activate on next programmed event.  If it is supposed to turn OFF, it will stay OFF.  If supposed to turn ON it will Turn ON.

In Auto Mode, it will remain in the current Mode OFF or ON until the next event after setting the timer.

If the battery voltage is low, then the numbers on the clock face are absent or very light gray. This means the any programming of events will be lost.  Timer can be cleared of all programming with the small RESET button next to the clock face.

If the Timer can draw a continuous 12 volts, then the programming is retained, even if the battery is removed.  However, if the battery is weak or failed and the circuit breakers are switched off for maintenance, all programming is lost.

The battery IS NOT recharged from the power circuits.  If it is weak, it must be replaced.