The battery is usually found under the hood, but it can also be found in the trunk of some vehicles. If the battery has no guide marks, the liquid should only cover the parts that are visible when the top or tops are removed. Prevent corrosion by smearing petroleum jelly or special battery jelly on the battery terminals. If the battery dies, use a mains power source to recharge it.
Check that the terminals are properly connected and that current is flowing through the charger’s ammeter. Disconnect the battery first if the vehicle has an alternator. A hydrometer can provide some insight into the state of the battery’s charger, but the reading will vary depending on the condition of the battery. Suck some liquid into the instrument by squeezing and releasing the bulb, then check the liquid level.