Your car battery is the power supply for all of the car's electronics and it starts the engine. Most car batteries are 12V and have 6 individual cells. Some car batteries have vent caps on the top of the case that can be removed to check and fill the electrolyte fluid inside.
Turn the car engine off. Open the hood and support it with the prop rod.
Locate the battery. Clean the top surface to remove any dirt and debris with a rag or fresh water before removing the vent caps.
Remove the vent caps by turning them counter clockwise and look inside each cell. The fluid level should be just below the bottom of the vent hole, level with the filler ring, for each cell.
Using a battery fill jug, fill any low cells with distilled water to bring them up to the appropriate level.
Replace the vent caps. Clean up any spills with fresh water and allow the area to dry.
