Onboard Battery Level of this ESP32? Voltage divider / Battery level

[Mahko_Mahko]

While I abandoned the original project, I got back to this for another project and thought I’d drop some more details here as the info I found was a little scattered and confusing for a newbie…

Based on:

1. This article: ESP8266 battery level meter | ezContents blog,

2. This thread: ESPHome Battery Level Sensor,

3. These objectives and resistors I had:
   

   

4. Some help/checks from @ssieb over on Discord,

5. This board/schema
   

   

6. The ESPHome docs: Analog To Digital Sensor — ESPHome

7. This wiring
   

   

8. And this ESPHome config:

sensor:
  - platform: adc
    id: solar_plant_batt_voltage 
    pin: GPIO32
    attenuation: auto
    name: ${friendly_name} Battery Voltage
    update_interval: 1s
    accuracy_decimals: 1
    filters:
    #use moving median to smooth spikes
      - median:
          window_size: 10
          send_every: 10
          send_first_at: 10
      - delta: 0.1 #Only send values to HA if they change 
      - throttle: 30s #Limit values sent to Ha
#Convert the Voltage to a battery  level (%)
  - platform: copy
    source_id: solar_plant_batt_voltage
    id: solar_plant_batt_level
    icon: "mdi:battery"
    name: ${friendly_name} Battery Level
    unit_of_measurement: '%'
    accuracy_decimals: 1
    filters:
      - calibrate_linear:
      # Map from voltage to Battery level
          - 0.41 -> 0
          - 3.1 -> 100
      #Handle/cap boundaries
      - lambda: |
          if (x < 0) return 0; 
          else if (x > 100) return 100;
          else return (x);
      - delta: 0.5 #Only send values to HA if they change 
      - throttle: 30s #Limit values sent to Ha

I’m not really 100% if both of the black wires are required?
Only one ground is required.