All batteries, regardless of type, should be kept clean on the outside and should be kept tightly secured by a battery hold-down device. If this is not done, battery acid can leak out, shortening the life of the battery, make it discharge more quickly and the corrosive acid can eat away components under the hood. A battery that is not a maintenance-free type must be checked periodically for water level. A maintenance-free type battery cannot have water added to it, but it must also be checked for electrolyte level. This can be done by looking at the color of the "eye". If this battery is too low on electrolyte, it must be replaced.