Unknown reset to factory default

I used Xbee XB3 for my wireless handheld device for reading remote signal.
I have encountered a problem for a while. I could not find out why.
The handheld device is powered by battery. When the battery almost running out of power, then I change a new set of battery.
It seems also reset the xbee to factory default. then my system could work anymore.
Any one know why and can help me ?

Sounds like you are getting the radio below VMIN.

I have the same problem with Xb3-24Z8PT-J, did anyone solve it?