Motorola SMP-418 Replacement Battery 7.4V 1200mAh

Motorola SMP-418 / SMP-458 / SMP-468 — 7.4V Li-ion Replacement Battery (60Q135901-C)

This 7.4V, 1200mAh Li-ion battery replaces the OEM 60Q135901-C pack in the Motorola SMP-418, SMP-458, and SMP-468 portable two-way radios. It fits directly into the factory battery bay and connects through the same three-contact interface the dock and radio use for charging and BMS communication. Capacity is 1200mAh (8.88Wh), matching the original specification.

• SMP-418 / SMP-458 / SMP-468 platform fit: All three models share the same battery bay geometry, contact pitch, and BMS handshake protocol — one pack covers the full SMP series without modification or adapters.
• Bench tested on actual hardware: We cycled this pack through charge and discharge on the SMP platform. The BMS accepted the charge current without tripping, held voltage through a sustained transmit load, and reported correctly to the radio's bar indicator at each threshold.
• First insertion into the charger dock: If the dock shows a fault LED on the first seating, remove the pack, wipe the three gold contacts with a dry cloth, and reseat firmly. The SMP charger requires a clean contact cycle to complete the BMS handshake before it will begin charging.

Why the SMP-418 cuts out mid-transmission on a freshly inserted pack

When a new Li-ion pack arrives from storage, its resting voltage is typically around 3.7–3.8V per cell — well within spec, but below the fully charged 4.2V per cell. The SMP radio's BMS monitors voltage under transmit load, and if the cell voltage sags below the cutoff threshold during the current spike of a PTT press, the BMS trips and the radio drops the transmission. This is not a faulty pack — it's the expected behaviour of a cell that hasn't completed its first full charge. Charge the pack to 100% in the dock before the first use shift and the cutout stops.

Bar indicator showing one fewer bar than expected after a full charge

The SMP series uses fixed voltage thresholds to drive the bar indicator — each bar corresponds to a voltage band, not a percentage from a fuel gauge chip. A new cell's internal impedance is slightly higher before the first few cycles, which means the voltage under load reads lower than the open-circuit voltage suggests. The indicator drops a bar because the radio is reading loaded voltage, not resting voltage. After two or three full charge-discharge cycles, cell impedance drops and the indicator reads correctly — confirm by checking the dock LED shows solid green before judging bar count.