OnCourse SiRF Star III GPS Compatible Battery 3.7V 1800mAh Li-ion

OnCourse SiRF Star III — 3.7V Li-ion Replacement Battery

This is a 3.7V, 1800mAh Li-ion cell for OnCourse GPS navigators running the SiRF Star III chipset. It fits the specific form factor these portable navigation units require — 52.98 x 35.39 x 11.61mm. Fit this when the original cell no longer holds a charge or the unit shuts off unexpectedly during navigation.

• SiRF Star III platform fit: OnCourse units built around the SiRF Star III chipset share a common board layout and connector spec. This cell matches the voltage rail and physical footprint that platform requires — no adapter or modification needed.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on SiRF Star III hardware. The BMS responded correctly at both ends — no false cutoffs on charge, and discharge terminated cleanly at the low-voltage threshold without triggering a hard fault.
• Cold start after power interruption: After fitting this battery, power the unit on outdoors before driving. The GPS performs a cold start after any full power removal — first satellite acquisition takes 5 to 10 minutes. Subsequent warm starts drop back under a minute once the almanac data is rebuilt.

GPS accuracy reduced at low battery on SiRF Star III units

When cell voltage drops toward 3.4V, some SiRF Star III units dial back RF receiver sensitivity as a power-saving measure. The chip is still tracking satellites, but weaker signals get dropped first. This shows up as position drift or a reduced satellite count on the status screen. Keeping the cell above 3.6V under load prevents the receiver from entering that reduced-sensitivity mode.

Unit shuts off without warning during active navigation

The battery indicator on these navigators reads voltage under no load — it does not account for the voltage sag caused by the GPS receiver and backlit display running together. A cell showing 30% can hit the low-voltage cutoff threshold under full draw before the indicator drops another bar. This is a calibration gap between the indicator and the actual cutoff point. If this is happening, treat the first battery warning as near-empty and plug into USB power rather than waiting for a second alert.