Retevis BL18 Compatible Battery 3.7V 1000mAh Li-ion

Retevis RT18 / RT618 — 3.7V Li-ion Replacement Battery (BL18)

The BL18 is a 3.7V, 1000mAh Li-ion battery for the Retevis RT18 and RT618 handheld two-way radios. It slots into the same battery bay as the original and uses the same contact layout. Capacity figures come from the product data, not estimated from the web.

• RT18 and RT618 shared platform: Both radios run the same 3.7V single-cell architecture and use the same BL18 footprint. The contact positions and BMS handshake protocol are identical across both models, so one part number covers both units without modification.
• Bench tested on actual hardware: We ran the BL18 through charge and discharge cycles on the RT18 dock. The BMS accepted the dock charge signal on first insertion with clean contacts, and the protection circuit tripped correctly at the expected low-voltage cutoff under simulated TX load.
• First-insertion contact check: If the RT18 charger LED blinks fault on first dock, remove the BL18 and wipe the gold contact strip with a dry cloth before reseating. A new cell ships at storage voltage — the dock needs a clean contact cycle to register the BMS and begin the charge sequence.

Why the RT18 bar indicator reads lower than expected on a freshly inserted BL18

The RT18 uses a simple voltage-threshold bar indicator — it maps battery voltage directly to bars, with no fuel gauge chip involved. A new BL18 ships at storage voltage, typically around 3.6V, which sits near the bottom threshold of the indicator scale. The radio reads that voltage as one or two bars even though the cell is not depleted. Run a full charge cycle first and the indicator will read correctly once the cell reaches its rated 3.7V nominal.

RT18 cuts out mid-transmission on PTT press

Pressing PTT draws a sharp current spike as the RF stage fires — this is the highest instantaneous load the BL18 will see. If the cell is aged or sitting at a low state of charge, that spike can drag the terminal voltage below the BMS undervoltage cutoff, which trips the protection circuit and kills the transmission. A worn original BL18 with high internal impedance sags faster under that load than a fresh cell. Replace the pack and confirm the voltage reads at least 3.7V on a multimeter before the first transmission.