About this replacement
Navman F15 / S45 — 3.7V Li-ion Replacement Battery (T300)
This is a 3.7V, 750mAh Li-ion replacement battery for the Navman F15 and S45 portable GPS navigators. It slots in where the original T300 cell sits and restores power to the device. Use this when the original battery no longer holds charge or causes unexpected shutdowns during navigation.
- F15 and S45 compatibility: Both the F15 and S45 share the same T300 battery footprint, voltage rail, and connector pinout. The BMS handshake on each device expects a 3.7V nominal cell — this replacement meets that spec without modification.
- Bench tested on actual hardware: We cycled this cell through charge and discharge on the F15 platform. The BMS accepted the cell immediately, completed a full charge cycle without fault, and drew down to the low-voltage cutoff without triggering a protection trip.
- First satellite fix after battery swap: After fitting this cell, power the unit on outdoors before your first drive. The GPS performs a cold start after any full power removal — first satellite acquisition takes 5–10 minutes. Subsequent warm starts return to under a minute once almanac data is cached.
GPS accuracy dropping at low battery on the F15
The F15 reduces receiver sensitivity as cell voltage drops toward the 3.2V threshold. This is a firmware-level power-saving measure, not a hardware fault. Position scatter and slower route recalculation both appear before the device shuts off. Keeping the battery above 3.5V during active navigation prevents the sensitivity reduction from engaging.
Device shuts off without a low-battery warning on the F15
After fitting a new cell, the fuel gauge on the F15 is uncalibrated against the new battery's discharge curve. The device's voltage-threshold indicator can hit the hardware cutoff before the on-screen warning fires. This resolves after one full charge-and-discharge cycle, which re-anchors the gauge to the actual cutoff point. Complete one full cycle — charge to 100%, run through active navigation until the device powers off — to calibrate.