My HR92 batteries (original factory supplied Alkaline) are lasting on average 18 months. I've just replaced the hallway and kitchen ones recently when they were generating multiple warnings in the fault logbook. In fact the hallway one went flat enough that the HR92 "crashed" with all symbols lit up on the screen at once and it was non-responsive.

The batteries in my CS92A were fine (1.5v is perfectly normal for Alkaline) and had only been in since October 2016, but it had started to give issues with overshoots and the occasional middle of the night comms fault from the sensor.

The battery drain of the CS92A should be very low - much lower than an HR92, however it (at least mine) seems to be a lot more sensitive to low voltage than an HR92, which will usually keep working until the battery can't turn the motor anymore...