Digi BL1800 user manual Batteries and External Battery Connections, 950 mA·h = 5.4 years 20 µA

C.2 Batteries and External Battery Connections

The soldered-in 950 mA·h lithium coin cell provides power to the real-time clock and SRAM when external power is removed from the circuit. This allows the Jackrabbit to continue to keep track of time and preserves the SRAM memory contents.

The drain on the battery is typically less than 20 µA when there is no external power applied. The battery can last more than 5 years:

950 mA·h

----------------------- = 5.4 years.

20 µA

The drain on the battery is typically less than 4 µA when there external power is applied. The battery can last for its full shelf life:

950 mA·h

------------------------ = 27 years (shelf life = 10 years).

4 µA

Since the shelf life of the battery is 10 years, the battery can last for its full shelf life when external power is applied to the Jackrabbit.

Header J2, shown in Figure C-4,allows external access to the battery. This header makes it possible to connect an external 3 V power supply while replacing the soldered-in 3 V lithium coin-type battery. This allows the Jackrabbit SRAM and real-time clock to retain data while the battery is being replaced.

		VBAT
J2 1		R1
EXT BATT	2	100 W
	3
	4

Figure C-4. External Battery Connections at Header J2

Alternatively, header J2 can be used to accommodate an external battery. In this case, be sure to cut out the soldered-in battery on the Jackrabbit to prevent discharging the external battery into a dead battery.

82 Jackrabbit (BL1800)