Rand McNally TND-T85 Replacement Battery 3.7V 4000mAh

Rand McNally TND-T85 — 3.7V Li-Polymer Replacement Battery (OP806363)

This 3.7V, 4000mAh Li-Polymer cell replaces the original OP806363 battery in the Rand McNally TND-T85 truck GPS navigator. It also fits the OD7, OD8, and PRO II 2 models, which share the same battery footprint and connector. Capacity figures come from the product data: 4000mAh / 14.8Wh.

• TND-T85, OD7, OD8, PRO II 2 compatibility: These four Rand McNally units run the same 3.7V power rail, use the same physical connector, and share the OP806363 cell dimensions — 65.00 × 61.50 × 7.80mm. No adapter or rewiring needed.
• Bench tested on actual hardware: We ran this cell through charge and discharge cycles on the TND-T85 platform. The BMS accepted the cell without fault codes, and the charge circuit cycled cleanly to full capacity.
• First satellite fix after power interruption: After fitting this cell, power the unit on outdoors and let it acquire a satellite fix before driving. A cold start after full power removal takes 5–10 minutes for first lock — normal behaviour. Subsequent warm starts return to under a minute.

Why the TND-T85 battery indicator drops fast under active navigation

The TND-T85 runs its GPS receiver, cellular traffic module, and backlit display simultaneously during active navigation. That combined draw pulls significantly more current than standby. An ageing or degraded original cell hits its voltage-sag threshold faster under load, so the indicator collapses quickly even from a full charge. A fresh 4000mAh cell restores the headroom needed to sustain that multi-component load without premature sag.

TND-T85 shuts off without warning before the battery indicator reaches empty

This happens when the fuel gauge calibration drifts after battery replacement. The device's charge indicator is calibrated to the original cell's discharge curve — a new cell may present a slightly different curve, and the unit cuts power before the visual warning triggers. To recalibrate, run the battery down to automatic shut-off twice, then charge uninterrupted to 100% each time. After two full cycles the indicator tracks accurately to the cell's actual 3.7V nominal floor.