I am working on a compact embedded project that can monitor the condition and behavior of a rechargeable battery while it is being used to power a portable electronic device. The main objective is to build a dedicated battery-monitoring module that can measure voltage, current, estimated remaining capacity, charging and discharging activity, and basic temperature information in real time. Instead of relying only on the battery percentage reported by a conventional operating system, the project is intended to collect actual electrical measurements and use them to estimate how the battery is behaving over repeated charge and discharge cycles. This is particularly useful for DIY electronics projects where a microcontroller, display, sensors, and other peripherals may have changing power requirements throughout the day. I want the monitor to operate as an independent layer between the battery and the main electronics, providing useful information without significantly affecting the available power. The system should also be small enough to eventually fit inside a custom enclosure, making it practical for portable devices, robotics projects, handheld instruments, or experimental power systems.

The hardware is being designed around a low-power microcontroller connected to a voltage-sensing circuit, a current measurement device, and a temperature sensor positioned close to the battery. Because directly measuring battery current can introduce unwanted voltage drop, I am evaluating different sensing approaches and paying particular attention to the resistance and thermal behavior of the measurement path. The voltage measurement circuit also needs appropriate scaling and protection so that the microcontroller's analog input remains within its safe operating range under all expected battery conditions. I am planning to include a small display or status interface that can show the instantaneous voltage, current direction, estimated capacity, and charging state. A few hardware indicators may also be used for situations such as low battery, abnormal temperature, or excessive current consumption. Another design consideration is power consumption by the monitor itself: there is little value in building an accurate battery monitor if the monitoring circuitry consumes enough energy to noticeably shorten the operating time of the device being monitored. For that reason, the controller will spend much of its time in low-power states and wake periodically to perform measurements.

The firmware will calculate more than just a simple battery percentage based on voltage. Battery voltage changes depending on load, temperature, charging state, and battery chemistry, so I am experimenting with combining voltage and current measurements with accumulated charge data to produce a more useful estimate. The controller will periodically sample the electrical measurements and calculate values such as instantaneous power and accumulated energy consumption. During charging, the firmware can identify the change in current direction and maintain separate information about charging and discharging behavior. A configurable sampling interval will allow the same hardware to be tested under different workloads without requiring firmware changes. I also want the firmware to recognize unusual measurement patterns, such as a sudden voltage drop under relatively high current, because this could provide useful information about battery resistance or an overloaded power system. Rather than immediately treating every unusual reading as a fault, the software will maintain short-term measurement history and use several consecutive samples before triggering a warning. This should reduce false alarms caused by temporary load changes.

One of the more challenging parts of the project is estimating battery capacity accurately over time. A nominal battery rating does not necessarily represent the amount of energy that will be available in every real-world situation, and the usable...