I think it has to be something related with some tricky naming convention in HA.
ESPhome has many more than just binary sensors. That yaml itself is an example of an analog sensor sending a float.
I suspect there’s gotta be something I can add to make HA render the value just like it does with my cellphone. 
Yes but only binary sensors support device classes in ESPHome. Sensors in ESPHome do not. Sensors in Home assistant do.
So format your battery sensor on the ESPHome device to output a % instead of a voltage. Then in home assistant customise that sensor by applying the battery device class. It has icons relating to battery state.
There is a provision in the ESPHome documentation, that talk to the possibly of measuring VCC. Perhaps you can try the abbreviated Yaml provide in their example. Pin used needs to be A0 only.
On the ESP8266 you can even measure the voltage the chip is getting. This can be useful in situations where you want to shut down the chip if the voltage is low when using a battery.
To measure the VCC voltage, set pin: to VCC and make sure nothing is connected to the A0 pin.
sensor: - platform: adc pin: VCC name: “VCC Voltage”
While that’s great for getting the battery voltage it does not answer the question:
Only adding the device class will do that.
Ok understood. It’s just strange that ESPHome can create ‘Wifi signal strength’ in HA using - platform: wifi_signal and does not for the - platform: adc Vcc value as both are usually considered as attributes. But Ok point taken.
That’s exactly right!!! Thank you @tom_l!!!
I did it on my esp_2 and it works!
Here is the final portion of that yaml:
- platform: adc
pin: VCC
id: "VCC"
internal: true
- platform: template
name: "esp.2.battery_level"
unit_of_measurement: '%'
update_interval: 5s
lambda: |-
return ((id(VCC).state /3.30) * 100.00);
Thank you!!!
Yeah, that was my thought as well, so I thought HA would just take it based on the ID or name, but nope… @tom_l was right, you have to override the class manually and make sure the value is in % and not V as I had it.
I hope this is a useful sample code for other people 
I’m getting the warning message when compiling it: warning: multi-line comment [-Wcomment]. Is a way arround the error message not to show up?
Thanks
It’s just a warning, forget it. I think that this small issue will be solved with next release
ok, thanks!
Hi I have a problem whit one of my d1 mini.
On one I can monitor the battery.
On the other one I get error.
Can some one help me whit this.
This is the yaml file:
esphome:
name: pool_thermometer
platform: ESP8266
board: d1_mini
wifi:
ssid: "xxxxxx"
password: "xxxxxxx"
# Enable fallback hotspot (captive portal) in case wifi connection fails
ap:
ssid: "Pool Thermometer"
password: "esdUJlWfq7B4"
dallas:
- pin: D7
sensor:
- platform: dallas
address: 0xED01193A97197128
name: "Poolen"
unit_of_measurement: "°C"
- platform: adc
pin: VCC
id: "VCC"
internal: true
- platform: template
name: "pool_thermometer_battery"
unit_of_measurement: '%'
update_interval: 60s
lambda: |-
return ((id(VCC).state /3.30) * 100.00);
captive_portal:
# Enable logging
logger:
# Enable Home Assistant API
api:
password: "xxx"
ota:
password: "xxxxxx"
Thanks
You are missing the name, it’s required. The ID is optional
---
platform: template
name: Level Battery ${devicename}
#device_class: battery
unit_of_measurement: '%'
accuracy_decimals: 0
id: ${devicename}_battery
update_interval: ${update_interval}
lambda: |-
return ((id(${devicename}_voltage).state /4.2) * 100.00);
// todo map only 3.0V to 4.2V as 0 to 100%, and up to 5V USB as 100%
can you help me to solve last line as lambda?
why is device_class not allowed?
thanks
Why did you choose 3.30 as the divisor? If my inkplate uses a 3.7v 1200mAH battery, should I make mine 3.7? Thanks in advance.
What I did was the following:
Minimum Voltage in my case is 3.0
Max voltage is: 4.2
for the lambda part:
lambda: |-
return ((id(${devicename}_voltage).state -3) /1.2 * 100.00);
In this case 3.0 V will be : 3-3= 0 /1.2 = 0 * 100= 0%
4.2-3 = 1.2/1.2 = 1 *100 = 100%
You can probably use the thing I just specified. 
Here my full code for measuring with A0:
sensor:
- platform: adc
pin: A0
id: "LIION"
name: "A0 Voltage x 4.2"
update_interval: 15s
accuracy_decimals: 3
filters:
- multiply: 4.2
- platform: template
name: "D1003_Battery_Voltage"
unit_of_measurement: 'V'
update_interval: 15s
accuracy_decimals: 2
lambda: |-
return (id(LIION).state);
- platform: template
name: "D1003_Battery_Percentage"
unit_of_measurement: '%'
update_interval: 15s
accuracy_decimals: 0
lambda: |-
return ((id(LIION).state-3) /1.2 * 100.00);
thank you for this!, it’s funny I was actually talking about trying to find out how to do exactly that 2hrs ago!
now i know!
thanks
Hey There,
thank you for this workaround. I hope ESPHome will have that sooner than later implemented itself.
I did what you wrote and created the costumization:
sensor.esp32_test1_battery_level:
device_class: battery
It did show up as a battery under devices correctely for a short time (until some variable updates in HASS i guess) and then it turned back to the default “Eye” Icon.
Does someone know why that happens?
Best regards
Florian
Did you ever get this figured out?