DIAGNOSIS The solid red LED indicates the battery or battery management system has entered a permanent protection state. Usually due to a deep discharge.
FIX First, ensure the battery is cool to the touch. Remove the battery from the vacuum by sliding the purple release latch. Plug the charger directly into the battery terminals. Leave it charging undisturbed for 6 hours minimum. Reattach to vacuum.
IF THAT DIDN'T WORK The battery may need a full power cycle. With the battery detached, press and hold the power button on the battery for 10 seconds. Reconnect to charger for 6 hours.
HEADS UP Continuously storing the vacuum with a depleted battery is the primary cause. Always store it on the dock or with some charge remaining.