To make sure everyone's talking about the same thing here: This difference in low battery sensitivity with CHDK vs without CHDK seems to only affect shutdown, not the warning icon. It started in bugsplatter's thread, here:
http://chdk.setepontos.com/index.php/topic,3872.
For the easiest way to test if your camera has this behavior in a noticeable amount, keep using your camera (with CHDK) normally. The next time it shuts down due to battery low and demands battery replacement/charging, restart the camera without CHDK and see if it will let you keep taking photos.
If it does, start CHDK and see if it will again shut down soon (in REC mode obviously, nearly empty batteries will run PLAY mode for ages). Then disable CHDK again etc etc, keep repeating until you're convinced that there either is or is not a noticeable difference.
People who know their way around an electronics lab can of course test quicker using an adjustable external power supply. Anyway, it's good to hear not all cameras are affected, at least not noticeably!
Those temperature ranges can be used for any type of battery, but it's quite understandable that they are not used in an AA cell a570, because it may be operated from a wide variety of cell chemistries (NiMH rechargables and non-rechargable alkaline and Lithium batteries being the usual suspects) and their temperature behavior is likely not similar enough.
For cameras with rechargable Lithium batteries specified by Canon, it's actually possible to know how temperature affects battery voltage, and use that information to make battery gauging more accurate. From whoever's IXUS950 table it would seem that battery warning may be enabled at a higher cell voltage when the battery is running hot than when it's cool. Some cameras may even lack the required temperature sensor, but all original lithium batteries will have one built in.
But if I'm not mistaken, this table is just a small part of the battery handling. For example, it's very probably these particular values have nothing to do with preventing lithium batteries from spontaneously combusting due to excessive temperature.
Oh and I do have some bad news too: I've now used the camera a bit more and it looks like I've only disabled one of the ways the camera uses to decide the battery to be weak. I still sometimes get the blinking battery icon after fiddling with the camera for a while longer than just a regular single shot even though my override values are not overwritten.
Maybe this table is just for a simple battery status deduction from threshold voltages, while more sophisticated voltage fluctuation/load monitoring may decide otherwise at a later time regardless of these values. In any case I'll keep using the patch since it does make the camera significantly less annoying as the battery icon never blinks right from the start like it otherwise would.
