I have had battery problems as well. I had to replace the battery on the contact sensor on my OHD in an unheated garage thrice. Twice on the motion sensor. The cold -30c (-22f) knocks the stuffing out of these little batteries. I finally decided to replace the stock battery with two AAA batteries in series (3v) and I also replaced a damaged reed switch with an external reed switch.
Works great now! Much bigger package though 
An odd thing I noticed.
When the contact sensor determines that the battery is low, it flashes the LED every couple of seconds. Which is sure to kill the battery even faster. . . But I guess that it figures that you have been notified and should just change the battery!
It’s not beautiful, but it works. 
Was -15c last night.
