Lithium-ion batteries are the cornerstone of modern electric mobility and renewable energy storage; however, they require strict monitoring to prevent catastrophic failures such as thermal runaway and deep discharge. This paper presents the design and hardware implementation of a modular Battery Management System (BMS) prototype. The system features a custom Analog Front-End (AFE) utilizing differential operational amplifiers for precise individual cell voltage monitoring and a Hall-effect sensor for current estimation. Furthermore, a hardware-based Constant Current/Constant Voltage (CC/CV) charging circuit was developed and tested. The prototype, validated using an Arduino microcontroller, achieved a voltage measurement accuracy of ±10mV and successful charge termination at 4.2V. This work serves as the foundational hardware layer for a future high-precision State-of-Charge (SoC) estimation system based on the Extended Kalman Filter (EKF).