Garmin GP55BT Compatible Battery 3.7V 800mAh Li-ion

TAKARA GP55BT — 3.7V Li-ion Replacement Battery

This is a 3.7V, 800mAh (2.96Wh) lithium-ion cell for the TAKARA GP55BT portable GPS navigator. It slots directly into the GP55BT battery bay and restores power to a unit that no longer holds a charge. Voltage and dimensions match the original: 47.90 × 44.10 × 5.55mm.

• GP55BT fit notes: The GP55BT uses a flat Li-ion cell at 3.7V with a compact form factor. The BMS on this replacement handles over-discharge cutoff and charge termination the same way the factory cell does — no firmware complaints or charge refusals during testing.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on the GP55BT platform. The BMS terminated charge cleanly at 4.2V and held cutoff voltage above 3.0V under load — no premature shutdowns observed during the run.
• First fix after swap: After fitting this cell, power the GPS fully on outdoors and let it acquire a satellite fix before use. The GP55BT performs a cold start after any full power interruption — first fix takes 5–10 minutes; subsequent warm starts drop to under a minute once almanac data is cached.

GPS accuracy reduced at low battery on the GP55BT

Some GPS units, including compact navigators in this class, step down receiver sensitivity when battery voltage drops toward the cutoff threshold. On the GP55BT, this can show up as position drift or slower fix updates before the low-battery indicator even appears. The receiver draws significant current — signal processing is one of the first things firmware throttles to extend run time. Keeping the cell above 3.6V under load avoids this behaviour.

GP55BT shuts off without warning — no low-battery alert first

This happens when the battery indicator is uncalibrated against the new cell's discharge curve. The GP55BT reads voltage to estimate remaining capacity, and an aged or replaced cell discharges differently than the curve the firmware expects. The unit hits its hardware cutoff voltage — typically around 3.0V — before the software low-battery alert triggers. Run two or three full charge-discharge cycles to let the firmware recalibrate its voltage-to-capacity estimate.