HmIP-STHO battery low vs battery plus sensor

[MelleD]

I have a Homeatic HmIP-STHO, which only has a binary sensor for the battery status and operating voltage. It uses two AA (1.5V) batteries.
So I entered the formula into the battery notes template.
{{(states('sensor.voltage')|float(0) / 3 * 100) | round(0) }}

Now my battery plus sensor still shows 77% at 2.3V. However, the Homeatic binary sensor says “battery low on.”

Am I doing something wrong?

[andrew-codechimp]

Hi, I assume the Homeatic binary low on sensor is one provided by the device itself?

If so it seems the device determines it's low when the voltage is still fairly high, the example template uses a linear scale (0v = 0%, 3v = 100%)

Something like this would work where 2.3v is 10% and 3v = 100%, clamped so that it is never less than 0
{{ [0, (((states('sensor.voltage')|float(0) - 2.3) / (3 - 2.3)) * 90 + 10) | round(0)] | max }}

I'd not thought about this before and it's interesting as many 3 volt devices would stop working well before even 1 volt. Please let me know how you get on with this and I'll add it to the documentation.

[MelleD]

Yes you are right it's from the device itself the low sensor, but there is no % sensor.

I'll try the new template and observe at what operating voltage it always goes low for the device sensor.
It's also an external sensor. I'm still trying to figure out what temperature it gets better at, because sometimes the low reading goes away again. I'll have to see if the operating voltage goes back up again when the outdoor temperature gets higher again

Thanks for the quick reply.

[MelleD]

Due to the outside temperature, I'm already experiencing a few fluctuations. Right now, I'm at 2.5V battery notes plus is 36%. So I think tomorrow morning when it gets colder, it will definitely be back at 2.3V, and then I'll see if it works.

[andrew-codechimp]

Temperature can really mess with battery voltages but if the 2.3v is not right just replace both the values to get something suitable for a low battery without too many false positives.

[MelleD]

Seems to work better in terms of the fill level, but the back and forth will probably remain the same. Hopefully it will be better after the replacement ;)

[andrew-codechimp]

Temperature fluctuations I can't do much about unfortunately.
Thanks for the feedback and raising the voltage to percentage issue, I've updated the documentation to help others in future.

[MelleD]

Temperature fluctuations I can't do much about unfortunately.

Yes off course :-). I just mentioned because you have more experience and maybe there are some ticks ;)