It’s important to regularly check the electrolyte (it really isn’t just water) level in your car’s battery, for two reasons: first, because it naturally evaporates and second, because a small amount electrolyzes into hydrogen and oxygen every time you charge the battery. Learning how to safely check and replace the water in your car battery is an important aspect of car maintenance. Start with Step 1 below for detailed instructions on how to check car battery water levels, while protecting both you and your car.
Locate the battery. In most cars, you simply need to open the hood of your car to access the battery.
Some batteries are located lower in the engine compartment, behind the front bumper and ahead of the front wheels. These are sometimes accessed from the bottom and need to be removed for service.
Most BMW and Mercedes Benz batteries and a few others are located in the trunk, concealed in an isolated compartment.
Batteries may also be located under the rear seat, such as in some Cadillacs.