I have seen this with the AirSTORM. I tried using some rechargeable 123A lithium cells thinking they would last for long periods of being powered off, but they didn't. Then I tried a regular lithium 2032 button cell and those were dead in a matter of several days. I thought they might heat up and explode because there does seem to be voltage at the RTC Vbackup, though the current must be extremely small because they didn't even get warm. That might explain why the relatively large lithium cells didn't really charge.

Since then I've moved to the recommended Lithium Vanadium Pentoxide rechargeable battery (http://wiki.gumstix.org/index.php?title=Coin_cell). It's very small, but seems to last as long as the others I've tried. Though I haven't conducted extensive testing yet. I have 10 units with this battery and I think I've only seen one go dead and loose the time after being powered off for about 3-4 days. The bottom line is these batteries should be lasting longer. I can leave a desktop PC unplugged for a month and a small battery will keep the RTC going, so what's the deal with these COM's?

At this point I have other projects to worry about, but I intend to investigate further when I can. If anyone can offer any other suggestions I would also be grateful.

-michael

On Aug 5, 2013 5:31 PM, "Nye, Philip" <Philip.Nye@acuitybrands.com> wrote:
I am getting reports of the system clock on the Gumstix (overo earth storm) losing big jumps of time - hours or days. This is most likely happening during power cycles though I have not been able to catch it happening. The overo is on our own board which has a non-rechargeable 3V lithium coin cell backing up the RTC.

Does anyone else have experience of anything like this? or pointers to what might be happening?

Is there anything in the backup battery circuitry which could cause the backup battery to drain at an abnormal rate? I know the circuit will trickle-charge a rechargeable cell and ours has a series diode to prevent unwanted back current.

Philip


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