The Rain Bird ESP-4M is an lawn sprinkler system which consists of a handheld electronic master control, underground plastic pipe and controllable 24-voltoperated sprinkler heads linked by buried wiring to the master control. You can program the controller of the sprinkler system of watering with a program.
Lithium Backup
The Rain Bird ESP-4M controller unit features an integrated lithium backup battery which keeps your watering program, date and the time in the event the power to the device goes out for any reason. The non-replaceable lithium battery, which has a promised service life of 5 to ten years, provides the controller unit’s memory until electrical power is restored to maintain its contents with a trickle of power. Without the lithium battery backup, your watering application would vanish if the AC power collapsed and you would need to program the system.
Secondly Battery
The ESP-4M controller permits you take it to some other place to unmount the programming faceplate and input a watering program or modify the program. The faceplate is powered by its standard 9-volt battery that was replaceable. The watering program saved in the memory of the controller is automatically upgraded, when you remount the faceplate.