Wednesday, January 30, 2008

Under hood Maintenance: Battery

Q & A: Battery

1. How can I tell if my battery is low and needs to recharged?

The first and most likely indication of a low battery would be a hard starting problem caused by slow cranking. If the battery seems weak or fails to crank your engine normally, it may be low. To find out, you need to check the battery's "state of charge."
A battery is nothing more than a chemical storage device for holding electrons until they're needed to crank the engine or run the lights or other electrical accessories on your vehicle. Checking the battery's state of charge will tell you how much juice the battery has available for such purposes.

If your battery is low, it needs to be recharged, not only to restore full power, but also to prevent possible damage to the battery. Ordinary automotive lead-acid storage batteries must be kept at or near full charge to keep the cell plates from becoming "sulfated" (a condition that occurs if the battery is run down and left in a discharged condition for more than a few days). As sulfate builds up, it reduces the battery's ability to hold a charge and supply voltage. Eventually the battery becomes useless and must be replaced.


The charge level depends on the concentration of acid inside the battery. The stronger the concentration of acid in the water, the higher the specific gravity of the solution, and the higher the state of charge.

On batteries with removable caps, state of charge can be checked with a "hydrometer." Some hydrometers have a calibrated float to measure the specific gravity of the acid solution while others simply have a number of colored balls. On the kind with a calibrated float, a hydrometer reading of 1.265 (corrected for temperature) indicates a fully charged battery, 1.230 indicates a 75% charge, 1.200 indicates a 50% charge, 1.170 indicates a 25% charge, and 1.140 or less indicates a discharged battery. On the kind that use floating balls, the number of balls that float tells you the approximate level of charge. All balls floating would indicate a fully charged battery, no balls floating would indicate a dead or fully discharged battery.

Some sealed-top batteries have a built-in hydrometer to indicate charge. The charge indicator only reads one cell, but usually shows the average charge for all battery cells. A green dot means the battery is 75% or more charged and is okay for use or further testing. No dot (a dark indicator) means the battery is low and should be recharged before it is returned to service or tested further. A clear or yellow indicator means the level of electrolyte inside has dropped too low, and the battery should be replaced.

On sealed-top batteries that do not have a built-in charge indicator, the state of charge can be determined by checking the battery's base or open circuit voltage with a digital voltmeter or multimeter. This is done by touching the meter leads to the positive and negative battery terminals while the ignition key is off.

A reading of 12.66 volts indicates a fully charged battery; 12.45 volts is 75% charged, 12.24 volts is 50% charged, and 12.06 volts is 25% charged.


CAUTION: Do not attempt to recharge a battery with low (or frozen) electrolyte! Doing so risks blowing up the battery if the hydrogen gas inside is ignited by a spark.

Your charging system should be capable of recharging the battery if it is not fully discharged. Thirty minutes or so of normal driving should be enough.

If your battery is completely dead or extremely low, it should be recharged with a fast or slow charger. This will reduce the risk of overtaxing and damaging your vehicle's charging system. One or both battery cables should be disconnected from the battery prior to charging it with a charger. This will eliminate any risk of damage to your vehicle's electrical system or its onboard electronics.


2. My battery keeps running down. Do I need a new battery?


It might, but then again it might not. The only way to know for sure is to (1) test the condition of the battery to see if it is capable of holding a charge, (2) check the output of the charging system to see if it is functioning properly, and (3) if the battery and charging system are okay, check for a possible current drain on the battery when the key is off. In other words, if the battery is okay and the charging system is doing its job, then something is draining voltage from the battery and running it down when the key is off.
One way to check the battery is to recharge it, then let it sit for a day with both battery cables disconnected. If the battery holds the charge and doesn't run down, it's probably okay, and the problem is in your charging system or wiring.

To see if the charging system is working properly, start the car and turn on the headlights. If the headlights are dim, it indicates the lights are running off the battery and that little or no juice is being produced by the alternator. If the lights get brighter as you rev the engine, it means the alternator is producing some current, but may not be producing enough at idle to keep the battery properly charged. If the lights have normal brightness and don't change intensity as the engine is revved, your charging system is functioning normally.

You can also check the charging system by connecting the leads of a voltmeter to the battery. When the engine starts, the charging voltage should jump to about 14.5 or higher. If the reading doesn't change or rises less than a volt, you have a charging problem that will require further diagnosis.

If the battery and charging system seem to be working normally, the only thing that's left is the electrical system. If the battery runs down overnight or when the vehicle sits for several days, it means something is remaining on and drawing current when the ignition is turned off. It may be a trunk light or cigarette lighter that remains on all the time, a fuel pump relay or other relay with frozen contacts that's drawing current, a rear window defroster that doesn't shut off, or a short in the radio or other electrical accessory.

All vehicles draw a little current from the battery when the key is off to run the clock, keep the memory alive in a digital radio (so it doesn't forget the station settings) and the engine computer. Alarm systems need current to keep their circuits armed as do cellular phones.

Current drain on the battery can be checked with an ammeter. Make sure the ignition is off, then disconnect one of the battery cables. Connect one ammeter lead to the battery and the other to the cable. The normal current drain on most vehicles should be about 25 milliamps or less. If the key-off drain exceeds 100 milliamps, there's an electrical problem that requires further diagnosis.

Finding the hidden current drain can be time consuming. The easiest way to isolate the problem is to pull one fuse at a time from the fuse panel until the ammeter reading drops. This will tell you which circuit is draining the battery. Then you have to check the wiring and each of the components in that circuit to pinpoint the problem.


3. How can I tell if my battery is good or bad?


The condition of the cell plates inside the battery determines whether or not a battery is still serviceable. Current is produced when sulfuric acid in the battery reacts with lead in the cell plates. As the battery discharges, sulfate accumulates on the plates and reduces the battery's ability to make current. The sulfate is returned to solution when the alternator recharges the battery by forcing current to flow in the opposite direction.
Over time, some of the sulfate becomes permanently attached to the plates. The sulfate forms a barrier that diminishes the battery's ability to produce and store electricity. This process can be accelerated if the battery is run down frequently or is allowed to remain in a discharged state for more than a few days. If the plates have become sulfated, therefore, the battery won't accept a charge and will have to be replaced.

Average battery life is only about four to five years under the best of circumstances -- and sometimes as short as two to three years in extremely hot climates such as Arizona and New Mexico. But the battery may become "sulfated" prematurely if it is chronically undercharged (charging problems or frequent short-trip driving), or if the water level inside the battery drops below the top of the cell plates as a result of hot weather or overcharging and allows the cell plates to dry out.


This is something you can't really do yourself, so you need to take your vehicle to a service facility that has the proper test equipment. The battery's condition can be determined one of two ways: with a carbon pile "load test" (that applies a calibrated load to the battery) or electronically with a special tester that measures the battery's internal resistance.

Equipment that uses a carbon pile for load testing requires the battery to be at least 75% charged. If the battery is less than 75% charged, a good battery may fail the test. So the state of charge must be checked first, and the battery recharged if it is low prior to testing. NOTE: The battery does NOT have to be fully charged prior to testing if an electronic tester that measures internal resistance is being used.

If load testing with a carbon pile, apply a load that is equal to half the battery's cold cranking amps (CCA) rating. A good battery should be able to supply half its CCA rating for fifteen seconds without dropping below 9.5 volts.


4. Does a replacement battery need to be the same size as my old one?

No. If your old battery has reached the end of the road and needs to be replaced, or if you think you need a battery with a bigger amp capacity for easier cold weather starting or to handle added electrical accessories (such as a killer stereo system, driving lights, etc.), then there's no reason why you have to install a battery that's the same size as your old one.
The word "size" may be a bit confusing here because what we're really talking about is the battery's amp or power rating, not the physical dimensions of its case.

A battery with a bigger case is not necessarily a more powerful battery. Battery manufacturers can cram a lot of amps into a relatively small box by varying the design of the cell plates and grids. So two batteries with identical exterior dimensions may have significantly different power ratings.

Batteries come in many different sizes and configurations (which are referred to as "group" sizes) because the vehicle manufacturers can't get together and standardize anything. So when you're choosing a battery, you have to consider three things: (1) the group size (height, width, length and post configuration), (2) whether your battery has top or side posts, and (3) how many amps will be needed for reliable cold starting and vehicle operation.


Because there are 57 different group sizes, many aftermarket replacement battery suppliers consolidate group sizes to simplify inventory requirements. So some replacement batteries may not fit exactly the same as the original. The battery may be slightly shorter, taller, narrower or wider than the original. But as long as it fits the battery tray and there are no interference problems (too tall a battery may cause the cables to make contact with the hood causing a dangerous and damaging electrical short!), it should work fine.

Some replacement batteries come with both side and top posts to further consolidate applications. Some also have folding handles to make handling and installation easier.


Though many replacement batteries are marketed by the number of "months" of warranty coverage provided (36, 48, 60, etc.), what's more important in terms of performance is the battery's power rating which is usually specified in "Cold Cranking Amps" (CCA) rating. The CCA rating tells you how many amps the battery can deliver at 0 degree F. for 30 seconds and still maintain a minimum voltage of 1.2v. per cell.

In the past, the rule of thumb was to always buy a battery with a rating of at least one CCA per cubic inch of engine displacement. But twice that is probably a better recommendation for reliable cold weather starting.

At the very least, you should buy a replacement battery with the same or better CCA rating as your old battery or one that meets the vehicle manufacturer's requirements. For most small four-cylinder engines, this would be a 450 CCA or larger battery, for a six cylinder application, a 550 CCA or larger battery, and for a V8 a 650 CCA or larger battery. Bigger is usually better. Extra battery capacity is recommended if your vehicle has a lot of electrical accessories such as air conditioning, power windows, seats, electric rear defogger, etc.


Most batteries are "dry charged" at the factory, which means they're activated as soon as acid is poured into the cells. Even so, the battery may require some charging to bring it all the way up to full charge.

Most experts recommend charging the battery before it is installed regardless of whether it is dry charged or not. This will ensure the battery is at full charge and lessen the strain on your charging system.

When the battery is installed, it must be locked down and held securely by a clamp, strap or bracket. This will not only keep the battery from sliding around on its tray (which might allow the positive cable to touch against something and short out the battery or start a fire!), but will also help to minimize vibration that can damage the battery.

The battery cables should also be inspected to make sure they're in good condition, too. If the cables are badly corroded, don't fit the battery posts or terminals tightly, or have been "fixed" by installing temporary clamps on the ends, the cables should be replaced. At the very least, you should clean the cable clamps and battery posts with a post cleaner, sandpaper or a wire brush to ensure good electrical contact. A light coating of grease, petroleum jelly and/or installing chemically treated felt washers under the cable clamps will help prevent corrosion.


5. Is there any danger to me or my vehicle if I give someone a "jump start?"


Yes. The danger to you is a battery explosion. Batteries contain hydrogen gas, which can ignite and explode if a spark occurs anywhere near the battery. Batteries also contain acid which may be splashed on you if the battery explodes.
The danger to your vehicle is if someone reverses the jumper connections or touches the jumper cables together. The voltage surge that results may damage your charging system and/or other electronic components in your vehicle.

To minimize these risks, use the following procedure when jump starting :

  • Do not smoke. You should also wear eye protection.
  • Make sure the vehicles are not touching (contact could provide an unwanted electrical path).
  • Turn your engine off.
  • Connect the red jumper cable from the positive (+) post or terminal on your "good" battery to the positive post or terminal on the low or dead battery in the other vehicle.
  • Connect the black jumper cable from the negative (-) post or terminal on your good battery to a solid ground on the other vehicle.
    CAUTION: DO NOT make the final jumper connection directly to the low or dead battery itself.

The reason for not doing this is because the final jumper connection usually produces a spark. Making the final connection away from the battery will minimize any danger of an explosion by keeping the spark well away from the battery.

  • Make sure the ground connection on the vehicle with the low or dead battery provides a good electrical contact. Use an unpainted metal surface like an engine bracket or a frame member.

  • Make sure the cables do not touch each other and that the cables are clear of the fan and pulleys on both vehicles.

  • Start the engine in the vehicle with the good battery. Run the engine at fast idle for several minutes before attempting to start the vehicle with the low or dead battery. This will allow the charging system to pump some life into the other battery lessening the drain on the good battery and charging system.

  • As soon as the vehicle with the dead battery starts, disconnect the battery cables. The vehicle should then be run or driven at least thirty minutes to recharge the low or dead battery. Additional charging time may be required depending on the battery's condition and state of charge.

If the vehicle does not crank or cranks slowly, recheck the jumper connections. If it still doesn't crank, the problem may be something other then the battery (such as a bad starter, solenoid, battery cable connection or internal engine problem).

If the vehicle cranks normally, but refuses to start, it may have an ignition, fuel or mechanical problem.

Do not crank the starter more than thirty seconds at a stretch. Allow the starter to cool for about two minutes before cranking the engine again. Continuous grinding of the starter can cause it to overheat and fail. Continuous cranking can also sap the juice out of your good battery and/or overload and possibly damage your charging system, too!

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