The NEEWER NW-P4 4 channel charger uses LED indicator lights for each charging slot to show the battery’s status:

Green Light (Input/Voltage Indicator):
The charger operates only when the green light is on. This indicates that a proper PD (Power Delivery) input is detected (usually 60W or higher). If you’re using a lower voltage power source (like 5V or 9V), the green light won’t turn on and the charger won’t work.​

Individual Slot LED Charging Indicators:
Each channel (battery slot) has an LED that provides real-time charging and battery status:

Red Light: The battery in that slot is currently charging.

Green Light: The battery in that slot is fully charged and ready for use.​

These indicator lights make it easy to see at a glance which batteries are charging and which are ready to go.

Summary:

Green input light = correct power supply detected, charger ready.​

Red slot light = charging; green slot light = fully charged.