[Nut-upsdev] REGRESSION: New "megatec" driver does't work for UPS that was managed by old fentonups driver

[Arjen de Korte]

> The problems with the battery charge calculation have been discussed
> before in this list, and I'm starting to agree with (I don't remember
> exactly who, sorry) who tried to convice me that having any kind of
> charge calculation was a bad idea.

That was me.

> I'm thinking if the charge calculation shouldn't be disabled by default...
>
> See, as simple as it is, the currenty way at least gives the user who
> can't read voltages some ideia of how charged is the UPS. At least, if
> the UPS happens to be on the known list. Complicating the calculation
> by adding more values to work with gives little benefit because the
> users would have to obtain these values themselves, and it is already
> difficult for them to obtain max:min now.

[soapbox]You can't calculate the battery charge by looking at the terminal
voltage.[/soapbox]

It may appear to be working for you, but only now. As soon as load,
temperature and/or battery age (!) change, the calculation will be off
(and more often than not by a landslide). The only way to accurately
measure the amount of charge in battery, is by keeping track of how much
charge is going in- and out of it and by regularly checking the amount of
total capacity it can hold. You'd still need some battery chemistry and
-manufacturer specific correction factors though, but vendors that
implement this usually know these.

Best regards, Arjen
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