Symmetra PX Charge percentage calculation

[ojfsdi]

How does Symmetra PX calculate charge percentage?

My PX has been displaying 89% now for over a day.  4 of the 32 battery cartridges are out, which is suspiciously close to 11% of the total battery capacity.

Does the PX measure voltage of each battery cartridge individually and contribute each cartridge towards one 32nd of 100%?  Or is there more to it?

[al_buffington]

Hi,

The number of batteries has no bearing on the battery capacity reading on the display. It is measuring the charge of the batteries that are installed as a whole. Removing batteries will only affect the displayed runtime. When you power up the UPS the battery charge percentage will report 80%. It will take approximately 6 hours (1% every 18 minutes) for it to reach 100.  Similarly,  if you were to  remove/install battery modules with the UPS running you would see a reset of the battery charge percentage. The new value (after the reset) would vary, but regardless would then start "charging" at the same rate as the initial power up (once the display reads 80%).  If you have not powered the UPS on/off or removed/installed battery modules, then it is not normal to see the charge level stuck at a value under 100. I seem to recall seeing another post of yours indicating that you may have changed the batteries inside some of the battery modules. Use of non-approved batteries would have an impact on the system's ability to effectively monitor the batteries.   

[ojfsdi]

Yes, we inherited this UPS after its previous owner replaced all of the batteries.  I don't think they ever did a runtime cal, and neither did we.  We're replacing batteries again now.

My charge percentage did make it up to 100% the next day.  I suspect that any time I eject and re-seat a battery or move a cartridge from one slot to another, it resets the charge percent.  Does that sound plausible?

[al_buffington]

Yes, that's correct. every time you remove/reinsert a battery the charge value will "reset". The calibration is only really necessary if you believe the displayed runtime is not accurate. Usually if old batteries are being replaced a calibration would be needed but some installations, especially those with generators, that never experience an extended outage would potentially not need it.