Had an interesting problem tonight.
I made a manual adjustment to the bathroom HR92 using the knob on the top, it started to turn for about a second, the backlight then went really dim (but not off) for a second then the motor stopped, the display went completely dead and the unit became unresponsive...
This HR92 is still on its original factory supplied batteries and has reported no low battery warnings and last time I checked was showing 2 bars on the battery indicator. It's about a year old.
I took the batteries out and refitted them and it came to life but it only showed a single bar on the battery indicator and the backlight was still somewhat dim. I tried taking them out and putting them back again - same problem.
Because it felt like there wasn't much "spring" in the battery contacts when I was closing the shorting strap across the top of the battery compartment I decided to try tensioning the spring contacts at the bottom of the batteries. If you remove it from the radiator you can actually get at the bottom of the contacts with a small screw driver from underneath and gently push them up a bit and bend them to give them a bit more spring, so I bent them up about 2mm.
I then put the batteries back in and could feel the obvious increase in springiness as I was clicking the shorting bar into place at the top - this time it booted up to show 2 bars of battery life as it should, the backlight was normal and everything seems fine again.
So it looks like the battery contacts at the bottom had insufficient tension on them... interesting in light of another post I will be making in a few days!
So the moral of the story is if your HR92 batteries don't seem to be lasting long at all in a particular unit, check the springiness and tension of the contacts below the batteries! There should be some movement and springiness to the batteries when you close and click the shorting bar at the top. If it just feels like it has come to rest against the batteries but not pushed them down a couple of millimetres, the contacts have lost their tension.