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Kurang Indikator Baterai (%) Gan!

External Display for Laptop Battery Percentage (From BMS)

1. What Battery Percentage Really Is

Laptop battery percentage is not measured directly from voltage or current. It is a software-calculated value produced by the Battery Management System (BMS).

  • Coulomb counting (current over time)
  • Voltage reference
  • Temperature compensation
  • Battery aging / health
  • Internal calibration tables

Only the BMS knows the real battery percentage.

2. How the BMS Communicates

The BMS does not talk to a screen. It communicates digitally inside the laptop: 

Battery → BMS → Embedded Controller → CPU → Windows

The display only shows what Windows already calculated.

3. Why External Battery Testers Cannot Be Used

External testers (electronic loads, ZB2L3, voltmeters) cannot be used while the battery is connected to a laptop.

  • Conflicts with laptop power-path management
  • Fights the internal BMS
  • Produces incorrect readings
  • Can damage the motherboard

External testers are ONLY for isolated batteries.

4. The Correct Architecture

Because battery percentage is a software result, it must be exported digitally, not electrically. 

Battery → BMS → Windows → Digital Interface → ESP32 → External Display

This is the same method used by manufacturers and diagnostic tools.

5. Getting Battery Data From Windows

Windows already reads BMS data through ACPI. Available data includes:

  • Battery percentage
  • Charging / discharging state
  • Design capacity
  • Full charge capacity
  • Cycle count

This data exists even if the laptop screen is not connected.

6. Showing Battery Percentage Without a Laptop Screen

The laptop only needs to boot. Battery data can be exported externally using:

  • USB (Serial)
  • Wi-Fi (HTTP)
  • Bluetooth (BLE)

7. Supported Transport Methods

USB (Serial) – Recommended

Windows → USB Serial → ESP32 → Display

Most stable and easiest to implement.

Wi-Fi (HTTP)

Windows → Wi-Fi → ESP32 → Display

Wireless and scalable.

Bluetooth (BLE)

Windows → BLE Battery Service → ESP32 → Display

Low power, hardest on Windows.

8. Why ESP32 Must NOT Touch the Battery

  • No direct battery wiring
  • No voltage-based estimation
  • No SMBus probing

Battery percentage is not an electrical signal.

9. ESP32 Role (Correct Design)

ESP32 acts only as a receiver and display device.

  • Receives battery data digitally
  • Displays percentage and status
  • Does not calculate battery values

10. Auto-Source Priority (Best Practice)

  1. USB
  2. Wi-Fi
  3. Bluetooth

ESP32 switches automatically without user interaction.

11. Safety Rules

  • Use OS-reported battery data only
  • Never connect external testers
  • Never probe battery communication lines

If the battery is inside the laptop, only the OS should read it.

12. Final Takeaway

Laptop battery percentage is a BMS software result. The only correct way to show it on an external display is to export it digitally from the operating system to an ESP32.

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