Please try one of the following options:
1. If the earphone and charging case are out of battery, charge them continuously for at least 2 hours to see if they charge fully.
2. Replace the cable and charger and check if this solves the issue.
3. Check if there is any dirt inside earbuds' copper pillars and the charging case's pogo pin.
4. Charge the earphone at an optimal charging temperature (about 25°C) and check if this solves the issue.
If the issue persists, please contact our Customer Support.