"Red light appearing on the top"に関する回答If the red light appears on the top of the toothbrush, you might have a slightly different model with a pressure sensor LED. See here: Is the Pressure Sensor Broken?
"Is the Pressure Sensor Broken?"に関する回答#1 If this only happens when the toothbrush is on, the pressure sensor plate doesn’t get a connection. It’s a a little metal spring with two contacts pressing against the motor housing and the contact opens if too much pressure is applied. Try cleaning these contacts and the opposing area if they still visibly connect. If they are bent, you might have to take apart the whole thing to straighten them. #2 I had a similar problem where the red light came on even with the toothbrush off, completely draining the battery over night. Opening it up, it seemed that the metal spring created a short between the upper frame and the battery. Wrapping the spring in some duct tape seems to have fixed that issue.