Here is the second part of the Battery FAQ written by Bill Darden. View Detailed Battery Maintenance : Part I

How do I install a battery?

A. Thoroughly wash and clean the old battery, battery terminals and case or tray with water to minimize problems from acid or corrosion. Heavy corrosion can be neutralized with a mixture of baking soda and water. Auto parts stores sell a cheep wire brush that will allow you to clean the inside of terminal clamps. Mark the positive cable so you do not forget which one it is when you reconnect.

B. Remove the NEGATIVE cable first, then POSITIVE cable and then the hold-down bracket or clamp. Dispose of the old battery by exchanging it when you buy your new one or at a recycling center. Batteries contain large amounts of lead and acid.

C. After removing the old battery, be sure that the battery tray and cable connectors are clean. If the cables are corroded or damaged, replace them; otherwise, they will significantly reduce starting capability.

D. Place the replacement battery so that the NEGATIVE cable will connect the NEGATIVE terminal. Reversing the polarity of the electrical system WILL severely damage it. E. After replacing the hold-down bracket, reconnect the POSITIVE cable first and then the NEGATIVE cable.

F. Before starting the engine, check the electrolyte levels and state-of-charge and refill or recharge as required.

G. Coat the terminals with a high temperature grease to prevent corrosion. If you do not want to lose your car's computer memory, security codes or radio settings, a second battery can be temporarily connected to the electrical system in parallel before disconnecting the first one. A cigarette lighter plug can easily connect a parallel battery.

How do I recharge my battery?

Some more words of caution. Do NOT ever disconnect a battery cable from the car with the engine running because the battery acts like a filter for the electrical system. Unfiltered electricity can damage the electrical components, for example, computer, radio, etc. (VERY important to BMW's computers GM)

Check the electrolyte level before recharging. Do NOT add water if the electrolyte is covering the top of the plates because during the recharging process, it will warm up and expand. After recharging has been completed and the electrolyte has cooled, RECHECK the level and add DISTILLED water to 1.8" BELOW the bottom of the filler tube (vent wells) or to the level indicated by the battery manufacturer.

Reinstall the vent caps before recharging and recharge ONLY in well ventilated areas. (NO smoking, sparks or open flames because while being recharged, batteries give off explosive gases.)

If your battery is sealed, do NOT recharge with high current. Usually, a car is jump started and run to recharge or "equalize" the battery, which might NOT fully charge it.

The length of time to fully recharge the battery depends on; the amount of discharge, the amount of surplus current that is diverted to the battery, how long the engine is run, RPM, and temperature. That is, an alternator is sized by the car manufacturer to carry the maximum accessory load and maintain a battery, NOT recharge a dead one.

If you have added audio amplifiers, alarms, cellular telephones or other accessories, the alternator might not produce enough current to keep your battery fully charged.

If you jump start your car, test your battery after you have finished driving it, and recharge it if the state-of-charge is below 75%. A better method to recharge batteries is to use an external constant current charger which is set not to deliver more than 1% of the CCA rating of the battery. The best method is to use an external constant voltage or tapered current charger. A constant voltage "automatic" charger applies regulated voltage at approximately 14.6 volts. A 10 amp automatic charger will cost between $30 and $50 at an auto parts store.

To prevent damage to the battery, the current should be less that 1% of the CCA rating during the first 30 minutes. With a taper charger, a high current, up to 30 amps, is applied to the battery for a short period up to 30 minutes maximum and then is regulated downward until the charge state reaches 100%. A 15 volt regulated power supply adjusted to 14.6 volts makes an excellent automatic battery charger.

For batteries with a state-of-charge of 35%, the following table, published by Interstate Batteries, lists the recommended battery charging rates and times:

Reserve Capacity (RC) ratingSlow Charge @ 5 AmpsFast Charge @ 20 Amps
80 min. or less10 hours2.5 hours
80-170 min.15 hours40 hours
125-170 min.22 hours5 hours

Can I increase the life of my battery?

Keeping your battery well maintained is the BEST way to extend the life of your battery. For cold climates, keeping the battery fully charged and warm will help. In the warmer climates and during the summer, the electrolyte levels need to be checked more frequently and DISTILLED water added, if required, due to the high under hood temperatures. Batteries last approximately two thirds as long in hot climates as cold ones. The parasitic load will determine how long a car can sit and will be started. Disconnecting the NEGATIVE cable will extend the "life" of the battery. Turning off unnecessary accessories and lights BEFORE starting your car will decrease the load on the battery while cranking. Leaving your lights or other accessories on and fully discharging the battery can ruin it, especially if it is the sealed or maintenance free type. Should this occur, you should test the battery after it has been recharged to determine if there is permanent damage. NEVER add acid -- just distilled water. Maintaining the correct electrolyte levels, tightening loose hold-down clamps and terminals, and removing corrosion is normally the ONLY preventative maintenance required for a battery.

What are the most common causes of premature battery failures?

  1. Loss of electrolyte due to underhood heat or overcharging
  2. Deep discharges (leaving your lights on)
  3. Using an undersized battery
  4. Undercharging
  5. Vibration
  6. Using tap water
  7. Corrosion
  8. Freezing

edited by Greg Mierz
Zundfolge - March 1996