About this replacement
Kirisun PT7200 / PT4208 — 7.4V Li-ion Replacement Battery (KB-70)
This is a 7.4V, 1700mAh Li-ion replacement battery for the Kirisun PT7200 and PT4208 portable two-way radios. It uses OEM part numbers KB-70 and KB-70B. Swap it in when the original pack no longer holds a charge through a full work shift.
- PT7200 and PT4208 platform fit: Both radios share the same battery bay dimensions, connector pinout, and BMS handshake protocol — one pack covers both units without any modification.
- Bench tested on actual hardware: We cycled this pack through transmit loads matching PTT duty cycles on the PT7200. The BMS held voltage rail above the radio's low-battery threshold across repeated TX bursts, and the protection circuit responded correctly to overcurrent events without locking out the pack.
- First insertion into the dock: If the charger shows a fault indication on first insert, remove the pack, wipe the gold contact strip with a dry cloth, and reseat firmly. The Kirisun dock requires a clean contact cycle to complete the BMS handshake before charging starts.
Why the PT7200 cuts out mid-transmission on a new KB-70 pack
New Li-ion cells ship at storage voltage — typically 3.6–3.7V per cell — not at full charge. When PTT is pressed, transmit current spikes sharply, and a cell sitting at storage voltage can momentarily sag below the radio's undervoltage cutoff. The radio interprets this as a depleted pack and drops the transmission. A full charge cycle before first use brings both cells to 4.2V and gives the BMS enough headroom to absorb that transmit spike cleanly.
Bar indicator reading one bar lower than expected after fitting a new pack
The PT7200 uses a simple voltage-threshold bar indicator — it reads resting cell voltage and maps it to bars. A pack at storage voltage sits in the two-bar range, not the three-bar range, so the display looks wrong even though the pack is not faulty. Charge the pack fully in the dock until the charge LED goes solid, then reinsert it into the radio. The bar indicator should read full at or above 8.2V resting.