The propane detector is generally connected to the battery directly. It will
always put a minor drain on the battery. If you leave the Roo unplugged for an extended period of time...the detector and other parasitic devices will drain the battery flat...even if everything you can turn off is turned off.
The solutions for storage can be to remove the negative wire from the battery or accomplish the same thing with a cut off on the battery terminal for under 10 bucks which is a LOT more convenient. See picture below.
Even when you've eliminate parasitic drain...you still have to consider self discharge which in summer months can average 15-20% per month. The answer is to take a battery reading ever couple of months so as NEVER to fall below the magic 50% charge. You may have already damaged the ablity of your batteries to HOLD a charge if they were flat enough to send you detector into tilt.
an check this by charging the batts FULLY for at least 8-10 hours THEN removing the negative wire for 24 hours. Then t
ake a voltage reading with a voltmeter. If it is less than 12.6 you have damage. If it is less than 12.4 you have significant damage. If it is 12.2 or less...you need new ones.