Rand McNally TND-T80B GPS Replacement Battery 3.7V 4000mAh

Rand McNally TND-T80B / TND-T80A — 3.7V Li-Polymer Replacement Battery (MLP3770110)

This 3.7V 4000mAh Li-Polymer cell replaces part number MLP3770110 in the Rand McNally TND-T80B and TND-T80A truck GPS navigators. Both units share the same battery bay dimensions and connector pinout. Capacity comes straight from the product data — 4000mAh, 14.8Wh.

• TND-T80B and TND-T80A compatibility: Both models run the same voltage rail and use the same MLP3770110 footprint. The BMS handshake is identical across the two, so one cell covers either unit without modification.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on the bench. The BMS held the charge cutoff at 4.2V and the low-voltage protection triggered cleanly before cell voltage dropped below safe floor. No thermal events observed.
• Cold-start satellite fix after power interruption: After fitting this cell, power the GPS fully on outdoors before driving. A full power removal clears the receiver's ephemeris cache, triggering a cold start. First satellite acquisition can take 5–10 minutes in open sky — subsequent warm starts run under a minute once that data is rebuilt.

GPS accuracy dropping at low battery on the TND-T80B

When cell voltage sags toward the low-voltage threshold, some GPS receivers reduce RF receiver sensitivity to cut power draw. On the TND-T80B, this shows up as position drift or a wider accuracy radius on the map — the satellite count stays the same but signal processing is degraded. Keeping the unit plugged into the cab's 12V supply during active navigation prevents this entirely. If running on battery only, watch for accuracy changes when the battery indicator hits the last segment.

TND-T80B shuts off without warning before the battery indicator reaches empty

This happens when the on-device fuel gauge is no longer calibrated to the actual cell. After a full battery swap, the gauge has no historical charge data to reference and can underestimate remaining capacity — or overestimate it, letting the device run until the BMS hard-cuts at minimum voltage. Run two or three full charge-to-cutoff cycles after fitting the new cell. This lets the firmware re-learn the cell's actual discharge curve and align the low-battery warning to trigger before the hard cutoff at 3.0V.