GM Buick/Oldsmobile/Pontiac/Full-Size 1975-1990 Repair Guide




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.


See Figure 1

Except Maintenance-Free Batteries

Batteries give off hydrogen gas which is explosive. Keep any spark or flame source away and DO NOT SMOKE around the battery! The battery electrolyte contains sulfuric acid; if you should splash any into your eyes or skin, flush with plenty of clear water and get immediate medical help.

Fill each cell to about 3 / 8 in. (9.5mm) above the tops of the plates. Always use distilled water (available in supermarkets or auto parts stores), because most tap water contains chemicals and minerals that may slowly damage the plates of your battery.

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Fig. Fig. 1: Correct battery water level.

Maintenance-Free Batteries

All later model cars are equipped with sealed maintenance-free batteries which do not require normal attention as far as fluid level checks are concerned. However, the terminals require periodic cleaning which should be performed at least once a year.


See Figures 2, 3, 4 and 5

Once a year, the battery terminal posts and the cable clamps should be cleaned. Loosen the clamp bolts (you may have to brush off any corrosion with a baking soda and water solution if they are really messy) and remove the cables, negative cable first. On batteries with posts on top, the use of a battery clamp puller is recommended. It is easy to break off a battery terminal if a clamp gets stuck without the puller. These pullers are inexpensive and available in most auto parts stores or auto departments. Side terminal battery cables are secured with a bolt.

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Fig. Fig. 2: Top terminal battery clamps may be removed with this inexpensive tool.

The best tool for battery clamp and terminal maintenance is a battery terminal brush. This inexpensive tool has a female ended wire brush for cleaning terminals, and a male ended wire brush inside for cleaning the insides of battery clamps. When using this tool, make sure you get both the terminal posts and the insides of the clamps nice and shiny. Any oxidation, corrosion or foreign material will prevent a sound electrical connection and inhibit either starting or charging. If your battery has side terminals, there is also a cleaning tool available for these.

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Fig. Fig. 3: Side terminal batteries require a small stiff wire brush.

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Fig. Fig. 4: Make sure both the clamps and terminal posts are cleaned until shiny.

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Fig. Fig. 5: An example of a battery cable in need of cleaning

Before installing the cables, remove the battery hold-down clamp or strap and remove the battery. Inspect the battery casing for leaks or cracks (which unfortunately can only be fixed by buying a new battery). Check the battery tray, wash it off with warm soapy water, rinse and dry. Any rust on the tray should be sanded away, and the tray given at least two coats of a quality anti-rust paint. Replace the battery, and install the hold-down clamp or strap, but do not overtighten.

Reinstall your clean battery cables, negative cable last. Tighten the cables on the terminal posts snugly; do not overtighten. Wipe a thin coat of petroleum jelly or grease all over the outside of the clamps. This will help to inhibit corrosion.

Finally, check the battery cables themselves. If the insulation of the cables is cracked or broken, or if the ends are frayed, replace the cable with a new cable of the same length and gauge.


Specific Gravity

See Figures 6 and 7

Check the specific gravity of the battery (your diesel has two) at every tune-up for gasoline engines and at every oil change for diesels. It should be between 1.20 and 1.30 at room temperature. The specific gravity is checked with a hydrometer, an inexpensive instrument available in most auto parts stores, auto departments and many hardware stores. The hydrometer looks like a turkey baster, having a rubber squeeze bulb on one end and a nozzle at the other. Insert the nozzle end into each battery cell and suck enough electrolyte (battery water) into the hydrometer to just lift the float. The specific gravity is then read by the graduations on the float. Some hydrometers are color coded, with each color signifying a certain range of specific gravity.

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Fig. Fig. 6: An inexpensive hydrometer will test the battery state of charge.

All cells of your battery should produce nearly equal specific gravity readings. Do not be extremely alarmed if all of your battery's cells are equally low (but check to see if your alternator belt is tight); however, a big difference between two or more cells should be a concern. Generally, if after charging, the specific gravity between any two cells varies more than 50 points (0.050), the battery is bad and should be replaced.

Batteries should be checked for proper electrolyte level at least once a month or more frequently. Keep a close eye on any cell or cells that are unusually low or seem to constantly need water. This may indicate a battery on its last legs, a leak, or a problem with the charging system.

The maintenance-free battery cannot be checked for charge by checking the specific gravity using a hand-held hydrometer. Instead, the built-in hydrometer must be used in order to determine the current state of charge. If the eye on top of the battery is dark, the battery electrolyte level is all right. If the eye is light, the electrolyte level is too low and the battery must be replaced.

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Fig. Fig. 7: Built-in hydrometer.

Load Testing

See Figures 8 and 9

  1. Connect a battery load tester and a voltmeter across the battery terminals (the battery cables should be disconnected from the battery). Apply a 300 amp load to the battery for 15 seconds to remove the surface charge. Remove the load.
  3. Wait 15 seconds to allow the battery to recover.
  5. Apply the appropriate test load for 15 seconds, as specified in the accompanying charts, while reading the voltage. Disconnect the load.
  7. Check the results against the appropriate chart. If the battery voltage was at or above the specified voltage for the temperature listed, the battery is good. If the voltage falls below what's listed, the battery should be replaced.

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Fig. Fig. 8: Appropriate test loads.

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Fig. Fig. 9: Minimum test voltages during load test.


Generally, a battery should be charged at a slow rate to keep the plates inside from getting too hot. However, if some 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. On maintenance-free batteries it may be necessary to tip the battery from side to side to get the green dot to appear after charging.

Charge the battery at the proper charging rate (amps) and time span.

75 amps - 40 min.
50 amps - 1 hr.
25 amps - 2hr.
10 amps - 5hr.

Always connect the battery charger according to manufacturers instructions.

Batteries naturally give off a certain amount of explosive hydrogen gas, more so when they are being charged. Keep any flame or spark source away from batteries at all times. Do not charge the battery for more than 50 amp/hours (to figure this, multiply the amps of the charging rate by the number of hours). If the green dot appears, or if electrolyte squirts out of the vent hole, stop the charge.


When battery replacement becomes necessary, select a battery with a rating equal to or greater than the one which was originally installed. Deterioration and 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 battery with greater capacity than the old one. Details on the role the battery plays in the vehicle's electrical systems are covered in Engine & Engine Overhaul of this information.

  1. Carefully disconnect the negative cable from the battery terminal.

Always use caution when working on or near the battery. Never allow a tool to bridge the gap between the negative and positive battery terminals. Also, do not wear metal watches or jewelry and be careful not to allow a tool to provide a ground between the positive cable and any metal component on the vehicle. Either of these conditions will cause a short leading to sparks and possibly, personal injury.

  1. With the negative battery cable disconnected and out of the way, carefully disconnect the positive cable from the battery terminal.
  3. Loosen the nut and/or bolt retaining the battery strap or clamp. Remove the battery retainer.
  5. Wearing an old pair of work gloves or using a battery lifting tool, carefully lift the battery out of the vehicle and place it in a safe location. Be sure to keep the battery from open flame and to protect surrounding areas from acid.

To install:
  1. Inspect the battery tray and cables for damage and corrosion. As necessary, clean or repair the tray and cables.
  3. Carefully lower the battery and position it in the tray, making sure not to allow the terminals to short on any bare metal during installation.
  5. Position and secure the battery retainer strap or clamp.
  7. Connect the positive cable to the positive battery terminal.
  9. Connect the negative cable to the negative battery terminal.