Battery Management Systems (BMSs) are essential for the safe, reliable, and efficient operation of rechargeable batteries because they supervise electrical, thermal, and operational conditions and support functions such as state-of-charge (SOC) estimation, protection, cell balancing, and diagnostics. The rapid adoption of Internet of Things (IoT) technologies has extended conventional BMS functionality by enabling wireless data transmission, cloud visualization, remote supervision, and event notification. This paper presents a systematic review of BMS architectures with emphasis on low-cost IoT-enabled implementations based on ESP32-class microcontrollers. The review covers voltage, current, and temperature acquisition; SOC and state-of-health (SOH) estimation; thermal protection; cell balancing; communication; cloud monitoring; and fault handling. Particular attention is given to an ESP32-based architecture using an INA219 voltage/current sensor, a DS18B20 temperature sensor, a local OLED display, a relay, a buzzer, and a Wi-Fi cloud interface. The reviewed literature indicates that ESP32-based systems can provide an economical platform for real-time monitoring, but a low-cost monitoring prototype should not be considered equivalent to a full multi-cell automotive BMS unless cell-level measurement, balancing, validated state estimation, robust protection circuitry, and safety-oriented communication are implemented. The paper identifies research gaps in accurate SOC/SOH estimation, multi-cell scalability, cybersecurity, fault diagnosis, and validation under dynamic operating conditions, and discusses directions toward predictive and intelligent BMSs