Furuno RC-1800F Operator's Manual page 376

Replacing Internal Battery
REF Offset Freq:
Synthe 1st Local:
RX 2nd Local:
Antenna Power Supply:
Temperature*:
Water Current*
Direction:
Speed:
Depth*:
Note: * requires data from the navigation device.
A lithium battery in the communication unit is used to backup system
settings. The life of this battery is about five years, however actual
life depends on usage when the battery is dead the communication
unit automatically reverts to default system settings. Contact you
dealer to request replacement of the battery.
Name: BTT(L1)
Code No.: 000-103-769
Type: CR1/2 8.L-F
Operating normally. If it does not light check
RX Synthesizer or REF OSC in the RF CON
Board. OK appears for figure less than 150.
Check of RF CON Board.
Check of RF CON Board 2nd local oscilla-
tor.
NG appears for discontinuity or short in cable.
Water temperature
Tidal current direction
Tidal current speed
Depth of water
8-9