WM Systems WMP 300 GPS Navigator Replacement Battery 3.7V 850mAh

WM Systems WMP 300 — 3.7V Li-Polymer Replacement Battery (BP85A)

This 3.7V 850mAh Li-Polymer cell replaces the original battery in the WM Systems WMP 300 and WMP-300 GPS navigator. It matches the OEM part number BP85A (1ICP7/31/52) and fits the same footprint at 51.80 × 30.22 × 5.70mm. Swap it in when the original cell no longer holds a charge or powers the unit through a full navigation session.

• WMP 300 / WMP-300 fit: Both model variants use the same board layout, connector, and 3.7V voltage rail. The BP85A cell works across both without modification — the BMS reads the same charge profile on either unit.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on a GPS navigator platform. The BMS accepted full charge without fault flags, and the protection circuit tripped correctly at the low-voltage cutoff threshold — no false shutoffs during normal draw.
• First-fix cold start after battery swap: After fitting this cell, power the WMP 300 fully on outdoors and let it acquire a satellite fix before relying on it. GPS units perform a cold start after any full power interruption — first fix can take 5–10 minutes while the receiver rebuilds its almanac. Subsequent warm starts run under a minute.

WMP 300 shutting off without warning at low battery

The WMP 300 battery indicator is calibrated against the original cell's discharge curve. A replacement cell with a slightly different curve can cause the unit to hit the hardware low-voltage cutoff before the on-screen warning triggers. The BMS cuts power at roughly 3.0V to protect the cell — the display may still show one bar at that point. Run two or three full charge-discharge cycles after fitting the new cell to let the device recalibrate its fuel gauge against the actual discharge curve.

GPS accuracy dropping during active navigation on this battery

Some GPS navigators reduce receiver sensitivity as battery voltage sags toward the low end of the discharge curve — this is a firmware power-saving measure, not a fault with the cell. If position accuracy drops noticeably mid-route, check the battery indicator. Above 3.5V the receiver runs at full sensitivity. Keeping screen brightness at mid-level during active navigation reduces total draw and keeps voltage higher for longer across the session.