HX684A that doesn't turn on and blinks battery and clean light rapdily

I have an HX684A (2 buttons)

When placed on the charger, the battery light and clean light blink rapidly. When I attempt to turn it on, it doesn’t react to any button presses. I tested the battery to see if it was a bad battery but after testing, it shows that the battery had 4.0 V coming out of it which I believe is the correct voltage. What could be the problem here? Any input would be much appreciated. Thanks in advance!