Translations:KAVAN Alpha 1500 V2 - Instruction manual/44/en

From KAVAN RC Wiki

Checking the transmitter battery

Turn on the transmitter and check the LED on the front panel – both the red and green have to glow. These LEDs indicate the status of the transmitter, not the transmitter battery voltage. The low-battery alarm is acoustic - once you hear beeping you have to land immediately and replace/recharge the batteries. If the transmitter beeps immediately after turning on, DO NOT try to fly at all.

Caution: Do not mix different types of batteries or accumulators or fresh batteries with (partly) discharged. Do not mix regular (zinc-carbon) batteries with alkaline batteries.