Nemerix BT77 Bluetooth GPS Replacement Battery HXE-W01 3.7V 1000mAh

Nemerix BT77 Bluetooth GPS Receiver — 3.7V Li-ion Replacement Battery (HXE-W01)

This is a 3.7V, 1000mAh Li-ion cell replacing the HXE-W01 in the Nemerix BT77 Bluetooth GPS Receiver. The BT77 is a compact portable GPS unit that streams location data over Bluetooth to a connected device. It runs on a single flat Li-ion cell housed behind the rear cover.

• BT77 platform fit: The BT77 uses a 3.7V single-cell architecture with a compact 52.96 x 33.64 x 5.15mm footprint. This cell matches that envelope and the connector orientation used on the original HXE-W01. The onboard BMS handles charge cutoff and over-discharge protection without requiring any handshake with the host device.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on a GPS receiver load profile — low continuous draw with periodic Bluetooth transmission bursts. The BMS held stable voltage across the full discharge curve with no unexpected cutoffs at the transmission peaks.
• Cold-start behaviour after fitting: After fitting this cell and powering on, take the BT77 outdoors immediately and leave it running. A full power interruption clears the GPS receiver's ephemeris data, triggering a cold start. First satellite fix after a cold start takes 5–10 minutes. Subsequent power cycles warm-start in under a minute once the almanac is cached.

GPS accuracy reduced at low battery on the BT77

When cell voltage drops below approximately 3.5V, some GPS receivers reduce RF front-end sensitivity to conserve power. On the BT77 this can show as wider position scatter or slower fix re-acquisition when moving. The symptom is easy to miss because the unit stays powered and appears to be working normally. A fresh, fully charged cell restores the receiver to full sensitivity immediately.

BT77 shutting off without warning before the battery indicator reaches empty

The BT77's battery indicator is calibrated against the original cell's discharge curve. After years of use, a degraded original cell may have a steeper voltage drop at end-of-life than the indicator expects, causing the device to cut power while still showing one bar. This replacement cell restores a standard discharge curve, but the indicator may still lag for the first two full charge-discharge cycles while the device recalibrates its threshold. Run two complete cycles — charge to full, use until shutdown — before trusting the indicator reading.