Battery life on X10 CM11A Computer Interface?

["Bruce W.1" <sorry@xxxxxxxxxxxxxxxxx>]

I got a CM11A computer interface from X10, it's a little white wall wart
box with a DB-9 cable to connect it to a PC and be programmed with the
ActiveHome software.

This device has two AAA batteries, the instructions say they are to
maintain memory if the power goes out.

In the ActiveHome software it says the batteries will last 500 hours,
that's about three weeks.  This conflicts with the instructions saying
it's just for power outages.  I'd hate to think I had to change its
batteries every three weeks when it's plugged into a 110VAC outlet.

Does anyone here have experience with battery life in this unit?  How
long do they last?

Thanks for your help.