<![CDATA[Automobile batteries require practical monitoring of voltage and current to support early identification of abnormal operating conditions. This study aimed to design and implement an Arduino Uno-based digital display system for monitoring a nominal 12 V automobile battery. The prototype integrates a resistor-divider voltage sensor, an ACS712-20A current sensor, an LM2596 DC-DC converter, a 16×2 I2C liquid-crystal display, and a buzzer. A Research and Development approach organized as an engineering design cycle was used, covering system design, prototype assembly, functional testing, and evaluation. Voltage readings were compared with a digital multimeter at five test points and produced a mean absolute percentage error of 0.38%. Current readings were examined under five charging and discharging conditions and produced a mean absolute percentage error of 3.61%; the largest relative deviation occurred at the lowest-magnitude discharge point. The buzzer remained off at 11.50 V and activated below 11.50 V, confirming the programmed comparator logic. The findings support the prototype as a simple continuous voltage-current and status monitoring device under the tested conditions. The study does not establish direct ampere-hour capacity or validated state-of-charge estimation; further validation with calibrated reference instruments, repeated measurements, multiple batteries, environmental variation, and dynamic automotive loads is required.]]>
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