Garmin Edge 305 Replacement Battery 361-00025-00 3.7V 850mAh

Garmin Edge 305 — 3.7V Li-ion Replacement Battery (361-00025-00)

This 3.7V 850mAh Li-ion cell replaces part number 361-00025-00 in the Garmin Edge 305 cycling GPS computer. It restores power to a device that tracks navigation, speed, distance, and performance data on the bike. Capacity matches the original 850mAh (3.15Wh) specification from Garmin.

• Edge 305 connector and form factor: The Edge 305 uses a single-cell Li-ion pack at 3.7V nominal with a fixed JST-style connector and a BMS that communicates charge state to the unit's fuel gauge. The cell must match the physical footprint — 50 x 34 x 5.50mm — to seat correctly under the rear cover without pressure on the PCB.
• Bench tested on actual hardware: We ran the cell through charge and discharge cycles on the Edge 305 platform. The BMS accepted the cell without error flags, the charge circuit terminated correctly at full voltage, and the fuel gauge registered accurately across the discharge curve.
• Cold-start satellite acquisition after swap: After fitting this cell, power the Edge 305 on outdoors in open sky and let it acquire a satellite fix before heading out. A full power interruption triggers a cold start — first fix can take 5 to 10 minutes. Subsequent warm starts drop back under a minute once the almanac is cached.

GPS accuracy reduced at low battery on the Edge 305

The Edge 305 receiver can reduce sensitivity as cell voltage drops toward the low-battery threshold. This shows up as position drift or track lines jumping off the road on the map display. It happens because the GPS RF front-end draws more current at full sensitivity than the BMS allows near cutoff. Keeping the cell charged above 3.6V maintains full receiver performance.

Edge 305 shutting off without warning at low charge

After a battery swap, the Edge 305 fuel gauge is uncalibrated to the new cell. The device may show two or three battery bars and cut off abruptly rather than stepping down through a low-battery warning. This is a calibration lag — the voltage-threshold indicator hasn't mapped the discharge curve of the new cell yet. Run two or three full charge-to-discharge cycles and the gauge tracks accurately, giving proper low-battery warnings before cutoff.