BQ27441 Rust Driver

A no_std Rust driver for the Texas Instruments BQ27441-G1 battery fuel gauge IC.

Features

• I²C Communication: Full support for blocking and async I²C operations
• Comprehensive Battery Monitoring:
  • State of Charge (SOC) - 0-100% (filtered/unfiltered)
  • Voltage measurements (mV)
  • Current measurements (mA)
  • Temperature readings (°C or 0.1K)
  • Remaining capacity and full charge capacity (mAh, filtered/unfiltered)
  • State of Health (SOH) percentage
  • Average power (mW)
• Power Management: Support for NORMAL, SLEEP, HIBERNATE, and SHUTDOWN modes
• Battery Configuration Workflow: Typed BatteryConfig (design capacity, OpConfig, current thresholds, safety/discharge/charge-termination alarms, Ra table) applied in one call via configure_battery(), which drives the full unseal → CONFIG UPDATE → apply → exit → reseal sequence for you
• Golden-File Snapshots: Read/write the calibrated Data Memory block set (GoldenSnapshot) used to back up or clone a tuned device
• Learning-Cycle Monitoring: learning_progress() and related helpers to track Impedance Track™ Qmax/Ra learning status
• Raw Data Memory Access: Block- and subclass-level read/write escape hatches for anything not covered by the typed config API
• Security: SEALED/UNSEALED modes
• YAML-Based Register Definitions: Uses the device-driver crate for type-safe register access
• Async Support: Optional async/await support via embedded-hal-async
• Smart Battery HAL: Bq27441Async implements embedded-batteries-async's SmartBattery trait
• Embassy Compatible: Works seamlessly with the Embassy framework
• defmt Support: Optional defmt logging for debugging

Hardware

The BQ27441-G1 is a System-Side Impedance Track™ Fuel Gauge for single-cell Li-Ion batteries.

• I²C Address: 0x55 (default)
• Supply Voltage: 1.8V - 3.6V
• Sense Resistor: Typically 10mΩ between SRN and SRP pins
• Variants:
  • BQ27441-G1A: For 4.2V maximum charge voltage batteries
  • BQ27441-G1B: For 4.3V or 4.35V maximum charge voltage batteries

Usage

Blocking I²C

use bq27441::Bq27441;
use embedded_hal::i2c::I2c;

// Create driver with default I2C address (0x55)
let mut gauge = Bq27441::new(i2c)?;

// Read battery status
let voltage = gauge.voltage()?;              // mV
let soc = gauge.state_of_charge()?;          // %
let capacity = gauge.remaining_capacity()?;  // mAh
let current = gauge.average_current()?;     // mA (signed)
let temp = gauge.temperature_celsius()?;     // °C

// Check charging status
if gauge.is_charging()? {
    println!("Battery is charging");
}

if gauge.is_full_charged()? {
    println!("Battery is fully charged");
}

Async I²C (with Embassy)

use bq27441::Bq27441Async;
use embedded_hal_async::i2c::I2c;

// Create async driver
let mut gauge = Bq27441Async::new(i2c).await?;

// Read battery status asynchronously
let voltage = gauge.voltage().await?;
let soc = gauge.state_of_charge().await?;
let capacity = gauge.remaining_capacity().await?;

embedded-batteries-async SmartBattery trait

With the async feature, Bq27441Async implements embedded_batteries_async::smart_battery::SmartBattery. Core measurements (voltage, SOC, capacity, temperature, status flags, design capacity) are mapped to the gauge registers. SBS commands the BQ27441 does not implement return Error::Unsupported.

use bq27441::Bq27441Async;
use embedded_batteries_async::smart_battery::SmartBattery;

async fn read_soc<I2C>(gauge: &mut Bq27441Async<I2C>) -> Result<u8, bq27441::Error<I2C::Error>>
where
    I2C: embedded_hal_async::i2c::I2c,
    I2C::Error: core::fmt::Debug,
{
    gauge.relative_state_of_charge().await
}

Configuring a New Battery

configure_battery() runs the whole CONFIG UPDATE workflow (unseal, enter config mode, write Data Memory, commit checksums, exit, reseal) in one call:

use bq27441::{BatteryConfig, ChemId, ConfigureOptions, BusyWait};

let config = BatteryConfig::for_chemistry(ChemId::G1A);
gauge.configure_battery(&config, ConfigureOptions::default(), &mut BusyWait)?;

Start from BatteryConfig::G1A_DEFAULT / BatteryConfig::G1B_DEFAULT (or for_chemistry) and override fields such as design_capacity_mah, current_thresholds, safety, discharge, charge_termination, or ra_table as needed. Use configure_battery_default() if you don't have your own DelayMs implementation. For manual control over the sequence, combine unseal(), enter_config_mode(), apply_battery_config(), and exit_config() yourself.

Golden-File Snapshots

// Back up a calibrated device
let snapshot = gauge.read_golden_snapshot()?;

// ...later, restore it onto another unit (device must be in CONFIG UPDATE mode)
gauge.write_golden_snapshot(snapshot, &mut BusyWait)?;

Learning-Cycle Monitoring

let progress = gauge.learning_progress()?;
if let Some(phase) = progress.phase() {
    println!("Learning phase: {phase:?}");
}

Manual Seal/Config-Mode Control

// Unseal device for configuration
gauge.unseal()?;

// Enter config update mode
gauge.enter_config_mode()?;

// Modify configuration via Data Memory
// (see `configure_battery`/`BatteryConfig` above, or use the raw
// `read_data_memory_block`/`write_data_memory_block` escape hatches)

// Exit config mode
gauge.exit_config_mode()?;

// Seal device to protect configuration
gauge.seal()?;

Examples

See the examples/ directory for complete working examples:

• stm32wba65ri_embassy.rs - Embassy async example for STM32WBA65RI

To run an example:

cargo build --example stm32wba65ri_embassy --features embassy --target thumbv8m.main-none-eabihf

API Overview

Core Methods

• voltage() - Read battery voltage in mV
• state_of_charge() / state_of_charge_unfiltered() - Read SOC percentage (0-100%)
• remaining_capacity() / remaining_capacity_unfiltered() / remaining_capacity_filtered() - Remaining capacity in mAh
• full_charge_capacity() / full_charge_capacity_unfiltered() / full_charge_capacity_filtered() - Full charge capacity in mAh
• nominal_available_capacity() / full_available_capacity() - Unfiltered capacity readings in mAh
• average_current() - Read average current in mA (signed)
• average_power() - Read average power in mW (signed)
• standby_current() / max_load_current() - Additional current readings in mA
• temperature_celsius() / internal_temperature_celsius() - Temperature in °C
• state_of_health() / state_of_health_status() - SOH percentage / decoded status

Status Methods

• is_battery_detected() - Check if battery is connected
• is_charging() / is_discharging() - Check charge direction
• is_full_charged() - Check if battery is fully charged
• is_over_temp() / is_under_temp() - Check temperature alarms
• needs_config_reload() - Check whether Data Memory needs to be re-applied
• flags() - Read all status flags

Control & Lifecycle Methods

• control_read(cmd) / control_write(cmd) - Send raw control subcommands
• control_status() / is_sealed() - Read decoded CONTROL_STATUS
• firmware_version() - Read firmware version
• chemistry_id() - Read chemistry ID (ChemId::G1A/G1B)
• seal() / unseal() - Enter/exit SEALED mode
• enter_config_mode() / exit_config_mode() / exit_config(ConfigExit) - CONFIG UPDATE mode control
• bat_insert() / bat_remove() - Battery presence signaling
• set_hibernate() / clear_hibernate() - Hibernate mode control
• shutdown_enable() / shutdown() - Shutdown mode control
• reset() / soft_reset() / pulse_gpout() - Device reset and GPOUT control

Configuration Methods

• read_battery_config() - Read the current BatteryConfig from Data Memory (unsealed)
• apply_battery_config(config) - Write a BatteryConfig while already in CONFIG UPDATE mode
• configure_battery(config, options, &mut delay) / configure_battery_default(config, options) - Full unseal/apply/reseal workflow
• read_golden_snapshot() / write_golden_snapshot(snapshot, &mut delay) - Back up/restore calibrated Data Memory
• read_data_memory_block() / write_data_memory_block() / read_data_memory_subclass() / write_data_memory_subclass() - Raw block/subclass access
• learning_progress() / update_status() / qmax_cell_0() / delta_voltage_mv() - Learning-cycle monitoring

Features

Enable optional features in your Cargo.toml:

[dependencies]
bq27441 = { version = "0.3", features = ["async", "defmt-03"] }

Available features:

• async - Enable async/await support (Bq27441Async), async config/golden/learning helpers, and embedded-batteries-async SmartBattery support
• defmt-03 - Enable defmt logging
• embassy - Enable both async and defmt (convenience feature)

Register Access

For low-level register access, use the .device() method:

// Access generated device API directly
let flags = gauge.device().flags().read()?;
if flags.bat_det() {
    println!("Battery detected");
}

Development

Building

# Build for embedded target
cargo build --target thumbv8m.main-none-eabihf

# Build with async support
cargo build --target thumbv8m.main-none-eabihf --features async

# Build with Embassy + defmt
cargo build --target thumbv8m.main-none-eabihf --features embassy

Register Definitions

Register definitions are maintained in src/bq27441.yaml using the device-driver crate's YAML format. The build script (build.rs) generates type-safe register access code at compile time.

Changelog

See CHANGELOG.md for release notes, including breaking changes.

License

The contents of this repository are dual-licensed under the MIT OR Apache 2.0 License. That means you can choose either the MIT license or the Apache 2.0 license when you re-use this code. See LICENSE-MIT or LICENSE-APACHE for more information on each specific license.

References

• BQ27441-G1 Datasheet
• BQ27441-G1 Technical Reference
• device-driver crate
• Embassy framework