Rand McNally TND-750 GPS Replacement Battery 3.7V 5000mAh

Rand McNally TND-750 — 3.7V Li-Polymer Replacement Battery (AHB865958)

This 3.7V, 5000mAh Li-Polymer cell replaces the AHB865958 battery in the Rand McNally TND-750 GPS navigator. The TND-750 is a truck and automotive navigation device that runs on internal battery power when disconnected from a vehicle power source. Fit this cell when the original no longer holds a charge or the device shuts down unexpectedly during use.

• TND-750 fit: The AHB865958 is the sole internal cell for this navigator. Voltage, connector pinout, and physical dimensions — 61.00 × 58.20 × 8.20mm — match the original exactly, so the device's charging circuit and low-battery indicator read the new cell correctly from first boot.
• Bench tested on actual hardware: We cycled this cell through charge and discharge passes on the TND-750 platform. The BMS accepted the cell without error flags, and the charge circuit reached full cutoff voltage at 4.2V as expected.
• Cold-start satellite acquisition after swap: After fitting this cell, power the TND-750 on outdoors and let it acquire a satellite fix before driving. The GPS performs a cold start after any full power interruption — first fix typically takes 5–10 minutes, compared to under a minute on a warm start.

GPS accuracy dropping at low battery on the TND-750

Some GPS units reduce receiver sensitivity as battery voltage drops, prioritising power conservation over signal strength. On the TND-750 this can show up as position drift or slower route recalculation near the end of a charge cycle. The fix is straightforward: keep the device charged above 20% during active navigation. If accuracy issues appear mid-route, connect the device to vehicle power — the GPS receiver will restore full sensitivity within a few seconds of stable voltage.

TND-750 shutting off without warning before the battery indicator hits empty

After a full battery swap, the TND-750's fuel gauge is uncalibrated — it has no charge history for the new cell. The device may cut power abruptly at what looks like 15–20% remaining because the low-battery threshold was mapped to the old, degraded cell's discharge curve. Run two full charge-to-discharge cycles to let the firmware recalibrate the indicator against the new cell's actual capacity. After that, the low-battery warning will trigger at the correct voltage, which is approximately 3.5V under load for this chemistry.