Rand McNally TND-720 Compatible Battery 3.7V 1500mAh

Rand McNally TND-720 — 3.7V Li-Polymer Replacement Battery (MLP643956)

This is a 3.7V 1500mAh Li-Polymer cell that replaces the original MLP643956 battery in the Rand McNally TND-720 truck GPS navigator. It fits the TND-720 directly, restoring power to the portable navigation unit. Voltage and cell dimensions match the original: 56.80 × 38.20 × 6.40mm.

• TND-720 fit confirmation: The TND-720 uses a single flat Li-Polymer pouch cell on a 3.7V rail. This replacement matches that rail voltage and the connector orientation so the BMS handshake completes without error codes on startup.
• Bench tested on actual hardware: We cycled this cell through full charge and discharge on the TND-720 platform. The onboard BMS accepted the cell, reported accurate charge state, and held voltage above the low-battery cutoff threshold through a complete navigation session.
• Cold-start satellite acquisition after swap: After fitting this cell, power the TND-720 on outdoors with a clear sky view before your first drive. A full power interruption clears the GPS receiver's warm-start cache, so the first satellite fix takes 5–10 minutes. Subsequent fixes return to under a minute once the almanac data is rebuilt.

GPS accuracy reduced at low battery on the TND-720

When cell voltage drops toward 3.4V, the TND-720 reduces power to the GPS receiver module to extend operation. Lower receiver power means weaker signal processing, which can cause position drift or delayed map updates during active navigation. This is a firmware-level power management decision, not a hardware fault. Keeping the unit plugged into the truck's 12V outlet during navigation eliminates the issue entirely — the battery then acts as a backup rather than the primary power source.

TND-720 shuts off without warning before the low-battery indicator appears

After a battery swap, the TND-720's fuel gauge IC needs one full charge-discharge cycle to recalibrate its voltage-to-capacity curve. Until that cycle runs, the displayed charge percentage can read 15–20% while the actual cell voltage is already at the hard cutoff threshold of approximately 3.0V. The device then shuts off with no visual warning. Run one complete charge from flat to full after fitting this cell to resync the gauge, and the low-battery warning will appear at the correct point going forward.