To ensure the safe operation of traction batteries, regular inspections are required. It is essential to pay attention to any signs of deterioration and perform appropriate repairs, especially in cases of electrolyte leakage and insulation damage. Battery condition checks can be combined with regular maintenance inspections, such as during electrolyte level refilling. Monitoring and checking the condition of batteries in use must be conducted according to the manufacturer’s instructions. Daily tasks include checking the electrolyte level and refilling it as necessary. A component that facilitates this inspection is the electrolyte level indicator. The device provides an optical signal when electrolyte refilling is needed. The level is refilled after charging to the designated level, e.g., using the Aqua water filling system.