XBee Supply Voltage dropping fast!

Oops… the Supply Voltage on my motion sensor is already down to 3060 millivolts. Suddenly it’s dropping very fast; this sensor has been operational for more then 7 weeks now, with IIRC 2 new and 1 older rechargeable battery of a brand with which i’ve had bad experiences before. I hope that’s what is causing this, cause if not, i have some work to do

The other 2 battery powered sensors are still doing fine, BTW:

Supply Voltages (click to view the realtime values)