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

[David R. <dav...@gm...>]

Hi Ted,

Thank you for the detailed explanation. That was very helpful, especially
the discussion of the battery constant and how it depends on having
sufficient load during calibration and self-tests.

Your point about lightly loaded Smart-UPS units not properly updating the
internal battery model makes a lot of sense, and it clarifies why
self-tests alone are not always sufficient to keep the battery state
accurate over time.

I appreciate you taking the time to spell this out so clearly. It is
exactly the kind of practical insight that makes this list valuable.

Best regards,
David

On Mon, Dec 29, 2025 at 5:02 PM Ted Mittelstaedt <te...@mi...>
wrote:

> 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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