Using atribute as a source for battery level

[PovilasID]

I have an MQTT sensor that has an atribute batteryLevel: 74.40945. It is a percentage value of 18650 type battery.
Can I use a an atribute as a source for manually defining a battery for a device?

[andrew-codechimp]

Hi, not seen one of those before.
You can add a helper percentage based on the attribute by following these instructions, just use a state_attr('xxx.xxx', 'batteryLevel')}} rather than state and round it to no decimal places.

[PovilasID]

Thanks, I guessed there must be option to retrieve an attribute did not think of the using a helper because for templates defined in the config you can not define a device association.

Have not seen 18650 batteries?
I have not seen them in consumer devices because they have much higher risk of catching on fire while being charged due different chemistry, however they can provide higher voltage and have higher capacity.
Also some cheaper models without protection can be discharged to a level that on next charge will catch fire (2 V or below) if not using a specific protocol and even then there is risk.
Monitoring battery health for these is much more important than any other battery types. It would actually be a good idea to add a disclaimer or warning next these if integration has an option for that.

[andrew-codechimp]

Yes, templates via the UI are far more useful these days with that ability to associate, it's just a shame there's that difference between the two methods but tying to an internal device id probably isn't a good idea for yaml in case it ever changes.

I meant I hadn't seen a percentage as an attribute but that's interesting about the 18650 batteries (and also one to avoid by the sounds of it!)
There's no way to add a disclaimer to a battery note but it's interesting, if I get more use cases I might think about this as a feature.

[PovilasID]

The inconsistencies in yaml definitions of sensnor: and template: got me a couple of times when I was setting up MQTT sensors initially. I understand how this happens yet this looks like one of these things that needs a rewrite eventually.

The percentage due to transmission protocol. I am using LoraWAN and it has built in battery value as a part of device status update message that I consume for device attributes because device status is not transmitted and does not change on every data transmission. LoraWAN is used in most smart (power/water) meters but consumers usually do not have encryption keys that utilities companies use to read these sensors.

18650 batteries are not dangerous because that is the same chemistry as in you laptop, phone, battery bank, electric scooter and EV. However, you may have noticed that most the devices mentioned do not allow you to replace the battery because you may chuck it in charger that may not have security features for safe charging. Hope some regulation enforces stricter standards so we take advantage of the tech. Every retailer selling 18650s has a disclaimer, you could probably just use if battery type is set as 18650.

For me it is about the capacity. I do not want to go down into a well every couple of weeks now I can go every couple of months.