Motorola NTN8971 Two-Way Radio Replacement Battery 4.8V 1200mAh

Motorola CP100 / 53871 Series — 4.8V Ni-MH Replacement Battery (NTN8971)

This is a 4.8V, 1200mAh Ni-MH battery pack for Motorola portable two-way radios including the CP100, 53871, Nextel I500 PLUS, and Nextel I550 series. It replaces OEM part numbers NTN8971, NNTN4190, NTN8657, NTN8970A, and several related variants. The pack slots into the same battery bay as the original and uses the same contact layout.

• CP100 and 53871 platform fit: These radios share a common battery bay geometry, contact pin arrangement, and 4.8V four-cell Ni-MH architecture. The BMS handshake protocol across this family is identical, so one pack covers all listed models without modification.
• Bench tested on actual hardware: We ran this pack through full charge and transmit-load cycles on a CP100 chassis. The BMS responded correctly to PTT-triggered current spikes and held voltage above the radio's low-battery threshold through sustained RF output cycles.
• First insertion into the charger dock: If the dock LED flashes fault on first insertion, remove the pack, wipe the gold contact strip with a dry cloth, and reseat firmly. The CP100 charging dock requires a clean contact cycle to complete the BMS handshake before it begins charging — a dirty or oxidised contact breaks that cycle.

Why the CP100 cuts out mid-transmission on a freshly inserted pack

Ni-MH cells ship at storage voltage — typically 1.0–1.1V per cell, which puts a four-cell pack around 4.2–4.4V total. The CP100 transmit circuit draws a sharp current spike the moment PTT is pressed. If the pack hasn't been charged first, that spike causes an immediate voltage sag that trips the radio's undervoltage cutoff, dropping the transmission. This is not a faulty battery — it's the BMS protecting cells that haven't yet reached operating charge. Charge the pack fully in the dock before first use in the field.

Bar indicator drops to one bar immediately after a full charge cycle

The CP100 and 53871 use a simple voltage-threshold bar indicator — each bar corresponds to a voltage band, not a percentage reading from a chip. A new Ni-MH pack can show surface charge immediately after the dock cycle, which briefly inflates the voltage reading, then settles to resting voltage once the pack equilibrates. If the bar drops after the radio has been on for a few minutes, check resting pack voltage with a multimeter — a fully charged 4.8V Ni-MH pack should read 5.4–5.6V at rest. Anything above 5.0V after a full dock cycle is within normal range.