The cordless vacuum will not start; the battery LEDs show a low-voltage error even after a full charge.

Safety first: Do not attempt to open the battery pack. Lithium batteries can be hazardous if punctured or shorted.

• Verify charger operation: Plug the official Numatic charger into a known-good outlet. Confirm that the charger indicator lights behave as described in the manual when the battery is docked.
• Extended charge: Leave the battery on the charger for several hours, even after it appears full. Some BMS systems perform cell balancing near full charge.
• Test with another charger or battery (if available): If another compatible charger is available, try it. If another battery works fine in the vacuum, your original pack is likely failing.
• Check storage conditions: If the battery has been unused for many months, it may have self-discharged below safe levels. In this case, replacement is usually required.

If the battery continues to show low-voltage error after proper charging, the pack is likely at end-of-life and should be replaced with a genuine Numatic battery.