feipoa wrote on 2021-06-09, 20:17:
Is it just me, or do some motherboards drain those CR2032 batteries substantially faster than other boards? It seems like I have a few boards in which the battery only lasts a year or two, whereas others last 10 years. Was there that much variance in the circuit (current draw) to hold the CMOS/clock settings?
ATX machines, if left plugged in while "off", have the capability of being able to maintain date and time and settings off the 5V standby supply, so in general, batteries in ATX should last longer than batteries in AT systems. That's not to say that they all take advantage of that.
Then you've got boards designed for the rechargables, where the board designer might have reasonably thought the machine would be used somewhat regularly, so he didn't take very much care on how many milliamps the clock/settings ate. Design from the beginning to use lithium cells may have taken more care.
The Dallas clock chips are meant to consume in the neighbourhood of a microwatt... if all the capacitances on the board store something like 100microwatt/hours, then you get 100 hours for free, this could go by a factor of 10 in either direction, according to how much capacitance there is, and whether it leaks through other sources, or remains while board is off. This would be why flipping the battery out and back in briefly without shorting the contacts or jumper provided, may not clear settings. Such a board you might only have to turn on twice a week to avoid it using the battery at all.
Then of course there's heat, it accelerates chemical reactions... including the self discharge rate of the battery... if it's sitting up cozy with the CPU at a constant 40-50C it might not last all that long even if the machine is seldom off... whereas if it's out by the edge of the board near some fresh air, it might be near ambient.
EDIT: Oh yah and some boards will stop the clock first to maintain settings as long as possible beyond a certain point of discharge, or that's just how it happens, the settings cling on at say 2V but the clock won't run.
Unicorn herding operations are proceeding, but all the totes of hens teeth and barrels of rocking horse poop give them plenty of hiding spots.