Charger immediately stops charging and indicates F3; the battery never reaches full charge.

Safety first: Unplug the charger and remove the battery. Do not attempt to open the battery pack.

• Retry charge: After 10-15 minutes, reconnect the battery and start charging again. Observe if F3 reappears immediately.
• Check battery age: If the battery is several years old or has seen heavy use, it may have reached its end of life.
• Compare with another battery: If another battery charges normally on the same charger, the original pack is defective.

F3 typically indicates an internal battery fault. Replace the battery pack with a genuine Hitachi replacement. Do not continue using a pack that repeatedly triggers F3.