Re: [Apcupsd-users] REPLACEBATT asserted despite normal charge and runtime estimate on Smart-UPS SMC1000C

[Ted M. <te...@mi...>]

Before writing off the battery pack I'd try running a calibration.

Since you are running an SMC you can't do it from apcupsd. Instead do 
the following:

1) Plug in a load like a resistance heater or something that runs the 
UPS at 60% load

2) Pull the plug on the UPS from the wall

3) Ignore the UPS beeping and wait until the battery pack is drained and 
the UPS shuts the heater off

4) Plug in the UPS and allow it to charge, then plug in your Linux box 
and fire up apcupsd.

Remember that the SmartUPSes do self-tests but those depend on the 
battery constant.  The battery constant changes as the battery ages but 
if there is not enough load on the UPS then the constant in the UPS 
won't get properly updated during self tests.  A common newbie UPS 
mistake is buying the highest capacity UPS you can lay your hands on 
then plugging something ridiculous like a single wall wart into the 
thing - assuming you have this massive battery compared to the load that 
will give hours of uptime to the wall wart and router running on it.

The battery constant is basically a variable related to the internal 
resistance of the battery.  As the battery ages it changes but if the 
UPS doesn't track that change it will get out of wack.

Note that you also need to do this process with a brand new battery.   
You plug the new battery pack in, give it a few hours to get fully good 
and charged, then run a calibration on it.


Ted


On 12/22/2025 8:45 PM, David Roth wrote:
> Hello all,
>
> I am running apcupsd 3.14.14 on Rocky Linux, monitoring an APC 
> Smart-UPS SMC1000C via USB.
>
> Recently, apcupsd began reporting:
>
> STATUS   : ONLINE REPLACEBATT
> BCHARGE  : 98.0 Percent
> TIMELEFT : 21.0 Minutes
> BATTV    : 27.0 Volts
>
> There has not been a recent real power outage, at least not within the 
> last month. Battery voltage appears nominal for a 24V system, and the 
> reported runtime estimate remains relatively high.
>
> The UPS manufacturing date, as reported on the unit label, is 2023. To 
> the best of my knowledge, these are the original batteries that 
> shipped with the UPS, which would make them approximately two years old.
>
> I have been using APC Smart-UPS units for many years and have not seen 
> this alert before. In the past, I typically replaced batteries only 
> after observing a clear history of declining runtime under load.
>
> My questions are:
>
> 1. What exact condition causes apcupsd to assert REPLACEBATT on 
> Smart-UPS models?
> 2. Is this flag driven primarily by internal battery age counters, 
> impedance tests, self-test results, or voltage behavior under load?
> 3. Is it expected for REPLACEBATT to appear even when TIMELEFT remains 
> strong?
> 4. Are there any apcupsd diagnostics beyond the standard status fields 
> that help distinguish an age-based warning from actual capacity 
> degradation?
>
> For reference, I intend to order a genuine APC APCRBC142 replacement 
> battery cartridge, but I wanted to better understand the logic behind 
> this flag and how apcupsd interprets it.
>
> Best regards,
>
> David Roth
>
>
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