Contact sensor 2nd gen battery keeps draining

I have 5 contact sensors and all of them are fine but one. The battery drains really fast and for about two days prior to a dead battery it will go from low battery to full battery back and forth until it is completely drained. Ive replaced the batteries on that sensor 5 times in the last month and a half. The other sensors are still at full. Ive even swapped the sensors around thinking it was the location i had it at and still same thing. It’s frustrating and annoying