Real‑Time Battery Monitoring with MAX17048 and ESP8266 via MQTT

Module Overview

The MAX17048 is a low‑cost, high‑accuracy fuel‑gauge designed for 3.7‑4.2 V Li‑polymer/ion cells. It provides real‑time voltage, state‑of‑charge (SOC), and charge/discharge rate readings. Two JST 2‑pin connectors allow simultaneous connection of the battery and a load/charger without additional switching circuitry.

Hardware Required

ESP8266 or ESP32 development board

MAX17048 module

18650 lithium‑ion cell (parallel connection only, never series)

Wiring Connections

Connect the ESP8266 pins to the MAX17048 as follows:

3.3 V → 3.3 V

GND → GND

D1 → SCL

D2 → SDA

Observe correct polarity; reversing the battery leads can damage the board.

Core API (Open‑Source)

Project repository: https://github.com/Priess0503/MQTT_18650_MAX17048

// Basic reads
float cellVoltage();   // battery voltage (V)
float cellPercent();   // SOC (%)
float chargeRate();    // charge/discharge rate (%/hr)

// Initialization
bool begin();
uint8_t getChipID();

// Power‑saving
void hibernate();
void wake();
bool isHibernating();

// Alerts
void setAlertVoltages(float minV, float maxV); // voltage thresholds
uint8_t getAlertStatus();
bool isActiveAlert();

MQTT Payload Example

{
  "voltage": 3.251,
  "soc": 18.5,
  "rate": -5.23,
  "state": "Discharging"
}

The rate field comes from the CRATE register; a negative value (e.g., -5.23%/hr) indicates the battery is discharging at 5.23 % per hour, while a positive value indicates charging.

Calibration and First‑Use

Before the first reading, fully charge the cell to 4.2 V. This triggers the quickStart routine, which calibrates the SOC value.

Verification

In a test the voltage read via MQTT was 4.13 V and SOC 91.8 %. A multimeter measurement confirmed these values, demonstrating the accuracy of the MAX17048 readings. With MQTT configured, battery status can be observed remotely at any time.