All batteries, regardless of type, should be kept tightly secured by a battery hold-down device. If this is not done, battery acid can leak out, making it discharge faster and leaking corrosive acid can eat away components under the hood. A battery that is not maintenance free must be checked periodically for electrolyte level. You cannot add water to a maintenance free battery, but it must also be checked for proper electrolyte level as indicated by the color of the "eye". Keep the top of the battery clean, as a film of dirt can sometimes completely discharge a battery that is not used for long periods. A solution of baking soda and water may be used for cleaning, but be careful to flush this off with clear water. DO NOT let any of the solution into the filler holes. Baking soda neutralizes battery acid and will de-activate a battery cell.
See Figure 1
Check the battery electrolyte level at least once a month, or more often in hot weather or during periods of extended vehicle operation. On non-maintenance free batteries, the level can be checked through the case on translucent batteries; the cell caps must be removed on other models. The electrolyte level in each cell should be kept filled to the split ring inside, or the line marked on the outside of the case.
If the level is low, add only distilled water through the opening until the level is correct. Each cell is completely separate from the others, so each must be checked and filled individually.
If water is added in freezing weather, the vehicle should be driven several miles to allow the water to mix with the electrolyte. Otherwise, the battery could freeze.
The electrolyte level on maintenance-free batteries is indicated by the color of the "eye", usually found on top of the battery. If this indicator appears to be clear or pale yellow in color, the battery should be replaced.
See Figures 2, 3, 4 and 5
Once a year (or as necessary), the battery terminals and the cable clamps should be cleaned. Loosen the clamps and remove the cables, negative cable first. On batteries with posts on top, the use of a puller specially made for the purpose is recommended. These are inexpensive, and available in auto parts stores. Side terminal battery cables are secured with a small bolt.
Clean the cable clamps and the battery terminal with a wire brush, until all corrosion, grease, etc., is removed and the metal is shiny. It is especially important to clean the inside of the clamp (an old knife is useful here) thoroughly, since a small deposit of foreign material or oxidation there will prevent a sound electrical connection and inhibit either starting or charging. Special tools are available for cleaning these parts, one type for conventional top post batteries and another type for side terminal batteries.
Before installing the cables, loosen the battery hold-down clamp or strap, remove the battery and check the battery tray. Clear it of any debris, and check it for soundness (battery tray can be cleaned with baking soda and water solution). Rust should be wire brushed away, and the metal given a couple coats of anti-rust paint. Install the battery and tighten the hold-down clamp or strap securely. Do not overtighten, as this can crack the battery case.
After the clamps and terminals are clean, reinstall the cables, negative cable last; DO NOT hammer on the clamps to install. Tighten the clamps securely, but do not distort them. Give the clamps and terminals a thin external coat of grease after installation, to retard corrosion.
Check the cables at the same time that the terminals are cleaned. If the cable insulation is cracked or broken, or if the ends are frayed, the cable should be replaced with a new cable of the same length and gauge.
See Figures 6 and 7
At least once a year, check the specific gravity of the battery. It should be between 1.20 and 1.26 in. Hg at room temperature. This test cannot be performed on maintenance free batteries in the usual way, instead the built-in indicator must be used.
The specific gravity of non-sealed (not maintenance free) batteries can be checked with the use of a hydrometer, an inexpensive instrument available from many sources, including auto parts stores. The hydrometer has squeeze bulb at one end and a nozzle at the other. Battery electrolyte is sucked into the hydrometer until the float is lifted from its seat. The specific gravity is then read by noting the position of the float. Generally, if after charging, the specific gravity between any two cells varies more than 50 points (0.50), the battery is bad and should be replaced.
It is not possible to check the specific gravity in this manner on sealed (maintenance free) batteries. Instead, the indicator built into the top of the case must be relied on to display any signs of battery deterioration. If the indicator is dark with a green (or similar color) dot in the center, the battery can be assumed to be OK. If the indicator is dark with no dot in the center, the specific gravity is low, and the battery should be charged or replaced.
A battery should be charged at a slow rate to keep the plates inside from getting too hot. However if some maintenance free batteries are allowed to discharge until they are almost "dead", they may have to be charged at a high rate to bring them back to "life". Always follow the battery charger manufacturer's instructions on charging the battery.
When it becomes necessary to replace the battery, select a battery with a rating equal to or greater than the battery originally installed. Deterioration and just plain aging of the battery cables, starter motor, and associated wires makes the battery's job harder in successive years. The slow increase in electrical resistance over time makes it prudent to install a new battery with a greater capacity than the old. Details on battery removal and installation are covered in Engine & Engine Overhaul .