Garmin GPS II Owner's Manual page 30

REFERENCE
24
Battery Level Indicator
The satellite status page also features a battery level indicator, located to the left of the
sky view, which displays the strength of the unit's batteries (Fig. 24).
The battery level indicator is calibrated for alkaline batteries. Ni-Cad and lithium
batteries will inaccurately display the battery level at one-half its proper level
!
due to voltage differences. No other receiver functions are affected by using Ni-
Cad or lithium batteries.
The GPS II features an internal lithium battery that will maintain the unit's memory
for up to 10 years, regardless of whether the four AA batteries are installed.
Fig. 24