Garnet SEELEVEL II 709-RVC Manual page 7

Note: If using two displays (i.e. a primary and a secondary display),
then only the primary display should have a connection to the
LPG tank. If both displays are connected to an LPG tank, then an
incorrect reading will result. The primary display relays LPG levels
to the secondary display through the sender wiring.
To read the battery voltage:
1. Press the BATT button and release it, the display will show the
battery voltage on the LED display.
2. If no other button is pressed, then the display will shut down
after about 5 seconds. If the BATT button is held down,
the display will continuously recheck the voltage and show
the updated value. The reading may flicker back and forth
between two values, for example, 12.6 and 12.7 volts. This is
normal behavior for a digital voltage display.
3. If another button is pressed before the 5 second time is up
for the BATT button, the display will immediately switch to
showing the value for the new button. The 5 second timeout
is restarted every time a button is pressed.
4. There is no hold mode for the battery voltage.
709-RVC Manual
Page 7