About this replacement
Garmin Foretrex 405 / 401 Series — 3.7V Li-Polymer Replacement Battery (361-00034-01)
This is a 3.7V, 290mAh Li-Polymer cell that replaces OEM part 361-00034-01 in the Garmin Foretrex 405, 405cx, and 401. It fits the wrist-mounted GPS navigator used in outdoor and tactical field applications. Dimensions are 29.50 × 24.30 × 4.80mm — measure your existing cell before fitting if you are unsure.
- Foretrex 405, 405cx, and 401 compatibility: All three models share the same battery bay dimensions, connector, and 3.7V supply rail. The 405cx adds a barometric altimeter, but the power circuit and battery interface are identical across the series.
- Bench tested on actual hardware: We cycled this cell through charge and discharge on the Foretrex platform. The BMS accepted the cell without error flags, voltage hold was consistent across GPS-active and standby states, and charge termination triggered cleanly at capacity.
- Cold-start reset after fitting: After fitting this cell, power the unit on outdoors and let it acquire a satellite fix before relying on it in the field. A full power interruption clears the GPS receiver's ephemeris cache, so expect a cold-start acquisition of 5–10 minutes on first use rather than the sub-minute warm start you are used to.
GPS accuracy reduced at low battery on the Foretrex 405
When cell voltage drops toward the lower end of its discharge curve, the Foretrex 405 reduces power to the GPS receiver to extend remaining operating time. This shows up as slower position updates and increased positional drift — not a faulty antenna or signal issue. A fresh cell running at nominal voltage restores full receiver sensitivity immediately. If you notice track logs becoming jagged before the low-battery indicator appears, the cell is likely sagging under receiver load.
Device shuts off without warning before the battery indicator hits empty
This happens when the battery indicator is calibrated against the original cell's discharge profile, and the replacement cell (or an aged original) has a steeper voltage drop under GPS load. The unit sees the voltage threshold for safe cutoff before the fuel gauge reaches the visual warning zone. To recalibrate, run the device from a full charge down to automatic shutdown twice without interruption. After two full cycles, the indicator aligns more accurately with actual remaining charge — the cutoff voltage is 3.0V on this platform.