[34S] battery warning indicator / question

[John Galt]

How do you determine when it's necessary to replace the two coin cells in a WP 34S?

I'm asking what people do in general practice. A description of the algorithm that activates the battery icon would be nice, if someone knowledgeable enough could describe it. It doesn't seem as useful as battery indicators in HP calculators, which can appear and remain visible for a long time before it's really necessary to replace them.

I suspect it is not possible to completely duplicate the behavior of the HP 30b battery indicator, but the usefulness of its implementation is less than ideal in the 34S.

The reason for asking is that it may appear briefly while doing a particularly demanding task, only to disappear later.

I'm not really concerned with losing information because I know how to back up to flash memory once in a while. I just want to know when others consider it's a good idea to replace the batteries: upon first noticing the battery indicator? When using BATT and noticing 2.9 or anything below 3? Something else?

Would it be possible (or would it even be desirable) to latch the battery indicator in software, so that once it appears it stays until the batteries are replaced?

Does HP use some super-secret algorithm that our resident 34S firmware programmers are unable to duplicate?

The problem is, if the batteries are somewhat depleted, the 34S will just crash without warning and "Restored" will appear. I am more motivated by curiosity than anything else, and am intentionally using weak batteries so I can understand how the calculator will fail when using them. I have also used a real power supply to determine the voltage at which the calculator will fail. The current can be limited but it's difficult for me to duplicate the behavior of real batteries that fail under load.