F7 appears and vacuum will not start; often after long storage.

Safety first: Do not attempt to jump‑start or open the battery pack.

• Charge for extended time: Connect the battery to the original OKP charger and leave it connected for at least 4–6 hours, even if LEDs do not light immediately. Some BMS circuits need time to recover.
• Try a different outlet/charger: Confirm the charger is working by testing with another OKP battery if available.
• Check storage conditions: If the battery was stored fully discharged for months, it is likely permanently damaged.
• Replace battery: If F7 remains and the battery will not accept charge, replace the OKP lithium‑ion battery pack. Dispose of the old pack at a proper battery recycling facility.