Retevis RT2 LB-75L Compatible Battery 7.4V 2000mAh

The RT2 charger dock blinks a fault LED the moment I insert the new LB-75L — it never starts charging. What's wrong?

The dock is rejecting the pack because the BMS handshake failed, usually due to a poor contact on the gold strip. Pull the pack out, wipe all gold contacts on both the pack and the dock with a dry cloth, then reseat the pack with firm, even pressure. If the fault LED clears and charging begins, the contact cycle is complete. If it persists, measure the pack voltage with a multimeter — a reading below 6.0V means the cells dropped below the dock's acceptance threshold during storage, and you'll need to trickle-charge the pack externally to 6.5V before the dock will accept it.

The RT2 drops to low transmit power partway through a long shift — battery shows two bars but RF output is weak. What causes that?

This is voltage sag under sustained RF load, not a depleted pack. As transmit current draws down the cells, terminal voltage dips below the RT2's high-power TX threshold even though resting voltage still reads two bars on the indicator. The pack is delivering voltage between transmissions but can't hold it under continuous load. Let the radio rest for several minutes to allow cell voltage to recover, then resume use with shorter PTT bursts. If sag occurs consistently in the first few charge cycles, run two full charge-discharge cycles to let the cells stabilise at rated capacity.

After the RT2 sat unused for several months with the LB-75L installed, the radio won't power on at all — is the battery dead?

Extended storage with the pack installed drains cells through the radio's standby current draw. If cell voltage fell below the BMS lockout threshold — roughly 5.8–6.0V for a 7.4V Li-ion pack — the BMS will block output entirely as a protection measure. Remove the pack from the radio and place it directly in the charger dock. A functional pack at low voltage will show a slow-blink charge LED rather than a fault LED; leave it on charge for a full cycle. If the dock shows no LED activity at all, measure pack voltage with a multimeter and compare against the 6.0V recovery floor.