Motorola SMP318 Two-Way Radio Replacement Battery 7.4V 1200mAh

Motorola SMP-318 — 7.4V Li-ion Replacement Battery (SMP318)

This 7.4V, 1200mAh Li-ion battery replaces the original pack in the Motorola SMP-318 portable two-way radio. It uses the same connector footprint and BMS handshake protocol as the factory cell, so the charger dock and radio firmware recognise it without modification. Dimensions are 90.20 × 56.40 × 26.40 mm — verify against your existing pack before ordering.

• SMP-318 platform fit: The SMP-318 draws transmit current in sharp spikes when PTT is pressed. The BMS in this pack is rated to handle those peaks without tripping into overcurrent lockout, which is the failure mode that kills cheaper cells fast on this radio.
• Bench tested on actual hardware: We cycled this pack through repeated PTT transmit loads on an SMP-318 bench unit and monitored the BMS response at each current spike. The protection circuit held stable across full charge-to-cutoff cycles without false trips.
• First insertion contact cycle: If the charger dock shows a fault LED on first insertion, remove the pack, wipe the gold contact strip with a dry cloth, and reseat firmly. The SMP-318 dock requires a clean contact cycle to complete the BMS handshake before charging begins.

Why the SMP-318 cuts out mid-transmission on a new battery

When PTT is pressed, the SMP-318 draws a sharp current spike to power the RF transmit stage. If the BMS interprets that spike as an overcurrent event, it trips and cuts power to the radio instantly. This looks like a dead battery or a faulty radio, but it is a BMS protection event. A new pack shipped at storage voltage — around 3.7V per cell — has lower headroom to absorb that spike than a fully charged pack does. Charge the battery to full before first use to bring both cells to 4.2V and reduce the risk of a BMS trip on the first transmission.

Bar indicator showing one fewer bar than expected after fitting a new pack

The SMP-318 reads battery level using voltage-threshold steps, not a fuel gauge chip. A new pack leaves the warehouse at storage voltage — typically 3.6–3.8V per cell — which sits at or below the threshold for the second bar. The radio is not misreading the battery; it is accurately reporting a cell that has not been charged yet. Place the pack in the dock, let it reach a full charge, and the bar indicator will update correctly once cell voltage crosses the upper threshold.