When charging the vacuum’s M18 battery, the Milwaukee charger LED flashes red and green alternately and the battery will not charge.

Safety first: Do not attempt to open or repair the battery pack. Damaged lithium packs can be hazardous.

• 1. Temperature check: If the battery is hot from use or very cold, let it sit at room temperature for 1–2 hours, then retry charging.
• 2. Clean terminals: Wipe the battery and charger contacts with a dry cloth to ensure good connection.
• 3. Try another charger: If available, test the battery on a different Milwaukee charger to rule out charger issues.
• 4. Compare with another battery: Charge a different M18 pack on the same charger. If only one pack fails, that pack is likely defective.
• 5. Replace battery: If the error persists, retire the faulty battery and replace it with a new genuine Milwaukee M18 pack. Recycle the old pack according to local regulations.