Does power fail when battery is dead and a TEST is run?

[jeffgus_apc]

This was originally posted on APC forums on 4/1/2015

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I have a client with an older Smart UPS 1500.  The battery does appear to be dead (this we know) but I was concerned to find out that it appears the power drops on this unit when a self test runs every 14 days.  Is that correct and by design that if the battery is dead the self test will still attempt to run and the power will fail to connected devices for that brief test period?  Of course we want to replace the battery but I would just hope that servers will not crash due to the Self Test if in fact the battery is dead.  Can anyone confirm this.....or should this NOT happen and maybe there is a problem with the unit.  If this does happen then we would need to make sure and disable the scheduled self tests whenever a unit has a bad battery to make sure it doesn't crash the servers on TEST before the battery is replaced.

Thanks

[Terry_Kennedy_apc · Accepted solution]

This was originally posted on APC forums on 4/2/2015

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Short answer: It will probably drop the load. If you have a management card or serial / USB cable you may be able to disable self-tests until you replace the battery.

Long answer:

The smaller UPS models (BackUPS / SmartUPS) will generally drop the load if the batteries are not detected as bad before the self-test runs. The reason for this is that the only thing the UPS knows about the batteries is the voltage they are at. Bad batteries can still read as normal voltage (12V for single-battery units, 12V or higher for multiple-battery models) until a load is applied, at which point the output voltage rapidly drops to zero - just like a flashlight that fades out almost immediately after you turn it on.

I don't know if these models "remember" this across self-tests. I would assume that this will light the "replace battery" LED and since the UPS knows the battery needs replacement, it shouldn't try to do another self-test. APC tech support could probably confirm this for a given UPS model if you asked them.

Higher-end models (Matrix and Symmetra) have more sophisticated monitoring. For example, in the SYBT2 pack, there are 10 batteries, 12V each. There's a sense wire in the middle (5 batteries on one side, 5 batteries on the other) which is reported to the UPS by the communication card. That's how the Symmetra knows which battery module is bad. There's support logic for temperature sensing in each SYBT2 battery pack as well, though I don't remember if it is actually stuffed with components.