-Charge till the red light off and can last for 120 days
-it is highly suggested to attach to the wall, fridge or place parallel to human body. not suggest to put them like under the cabinet, not enough space to sense body. but it it is ok to do so if you can guarantee there are enough space to sense human body
-No need battery !!!!! USD Rechargeable for use . more economic and cheaper in a long run!!