Does your car battery contain enough power to start your engine during cold weather. The only way to know if your battery is fully charged or not is to measure the battery's state of charge with a voltmeter. You can use an analog or digital voltmeter, but a digital meter is easier to read and will give you a more accurate reading. First, make sure the ignition key is OFF, and all the vehicle's lights are OFF. To check your battery's state of charge, connect the RED or POSITIVE voltmeter test lead to your battery POSITIVE terminal. The positive terminal will be marked with a PLUS symbol (+), and the battery cable that is connected to the positive terminal is often color coded RED. Connect the BLACK or NEGATIVE voltmeter test lead to your battery NEGATIVE terminal. The negative terminal will be marked with a minus symbol (-), and the battery cable that is connected to the negative terminal is often color coded BLACK. Note the reading on your voltmeter and refer to the chart below: Battery Voltage and State of Charge (at 80 degrees F): (NOTE: Subtract 0.024 volts for every 10 degree F drop in temperature) The photo at the top of this page shows a battery voltage reading of 12.29 volts, which means the battery being tested is low with only about half a charge. The battery needs to be recharged. Is Your Battery Low? If your battery voltage is less than 12.45 volts (75 percent charged), it is low and should be recharged. This can be done by connecting a portable battery charger to your battery, or by driving your car for 15 to 20 minutes at 40 mph or faster. Automotive lead-acid batteries should be maintained at a 75 percent charge level or higher for best performance and life. If the battery is allowed to run down and is not brought back up to 75 percent or higher charge within a few days, the battery may be permanently damaged. Sulfation can prevent the cell plates inside the battery from accepting a full charge. Over time, this will lead to diminished battery performance and life. Why You Need a Good Battery for Reliable Cold Weather Starting A good battery is essential for reliable starting, especially during cold weather because cold weather increases the cranking load on the battery. Oil gets thicker at low temperatures so it takes more amps to crank a cold engine when you try to start it. At 0 degrees F, the number of cranking amps it takes to start a cold engine may increase as much as 2X. At minus 15 degrees below zero F. , it can take 3X or more amps to crank the engine depending on the viscosity of the oil in the crankcase. The thicker the oil, the harder is it to crank the engine. At the same time, cold temperatures also sap the battery's ability to supply amps. At 0 degrees F, most batteries can only deliver about 65% of their normal cranking amps. At -20 degrees, battery power is cut in half! Warning: Do NOT attempt to recharge your battery if it has run down and the liquid inside is frozen. This may cause the battery to explode! Remove the battery and take it inside so it can thaw before recharging or testing it. How To Tell If Your Battery Is Good or Bad? A GOOD battery is one that will accept and hold a charge, and is capable of producing close to its rated amperage output. A BAD battery is one that will NOT accept or hold a charge, or cannot produce adequate cranking amps. A GOOD battery can be recharged and returned to service but a BAD battery needs to be replaced. Most wet cell lead-acid car batteries only last about 4 to 5 years, and may only last 2 or 3 years in a late model car that is not driven frequently enough or far enough to keep the battery fully charged. Hot climates can also shorten battery life to 2 to 3 years. If your battery is 4 or more years older and is not holding a charge (keeps running down), or it does not seem to crank your engine a normal speed, you probably need a new battery. Chronic undercharging can cause premature battery failure regardless of the age of the battery. Car batteries are not designed for deep discharge (running all the way down), unlike a marine and RV battery which can handle being fully discharged. If a car battery is run down and left in a discharged state for very long (say a week or more), the plates may become sulfated and not accept a full charge when the battery is recharged. Over time, this will diminish battery capacity and cause it to eventually fail. Undercharging can be the result of a faulty charging system (low charging voltage), or driving short distances during cold weather with lights, heater, heated seats, defrosters and radio all on. If the charging system can't replace the amps that your electrical system is using, your battery will gradually run down until eventually it won't start your car. Symptoms of a Low Battery: Slow cranking when attempting to start or no cranking at all. Unusual electrical problems such as the power windows not working normally, heated seats or electric defrosters not producing normal heat output, remote keyless entry not opening doors or trunk, etc. A low or dead battery does not mean your battery has failed, or that it needs to be replaced. A good battery can run down for any number of reasons: somebody left the lights on, you haven't been driving your vehicle enough to keep the battery fully charged, your vehicle has been sitting for a long period of time without being started, there is a problem with the charging system or alternator, or an electrical problem is draining power from the battery when your car is off. For these reasons, you need to test BOTH the battery and charging system. Battery Testing The only way to know if your battery is GOOD or BAD is to test it. Many auto parts stores will test your battery for free. If your vehicle is driveable or you can get it going with a jump start, drive to a nearby auto parts store that offers free testing and have them test your battery and charging system. If you can't get your car started, remove the battery and get a friend to give you a ride to the auto parts store so you can have the battery tested. Many repair shops will also test your battery and charging system, but they usually charge a fee for this service (some will test your battery for free or offer to apply their diagnostic fee towards the cost of repair). CAUTION: Conventional wet cell lead-acid car batteries are filled with a mixture of water and sulfuric acid. Wear gloves and handle the battery with care so no liquid spills on your skin or clothing. Battery acid can cause severe burns. If a spill does occur, wash with plenty of water and neutralize the acid by applying baking soda. AGM batteries do not contain any liquid, cannot spill and are safer to handle. There are essentially two ways to test a battery. The "old fashioned way" is to use a Load Tester. For accurate results with a load tester, the battery must first be recharged before it is tested. The tester applies a calibrated load to the battery (typically half the battery cold cranking amp [CCA] capacity or three times its amp/hour rating). While the load is applied, the tester monitors battery voltage. If the battery voltage drops below 9.6 volts during the test, the battery is BAD and needs to be replaced. If the voltage remains about 9.6 volts, the battery is GOOD and can be returned to service. The other (and must faster) method for testing your battery is to use an electronic "conductance" tester like the one shown here. A conductance tester sends a alternating frequency signal through the battery to determine the condition of the cell plates inside the battery. As a battery ages, its internal conductance declines. Shorts, opens and other cell defects also reduce conductance, so measuring conductance gives an accurate indication of battery condition. The best feature of this type of test is that the battery does NOT have to be recharged prior to testing. Most conductance testers will give an accurate reading even if the battery is almost dead. Some electronic battery testers can also analyze the battery's CCA capacity, which can be used to estimate the battery's remaining service life. Some testers can also measure the amps drawn by the starter while cranking the engine, and analyze charging system output under load once the engine is running. Some testers even provide a built-in voltmeter for checking connections. Bad Battery Connections If an electronic tester can calculate the battery/s CCA rating, it can also be used to diagnose bad ground connections. First the CCA capacity is tested at the battery terminal connections, then again using a ground point on the engine or elsewhere. More than a 25 percent difference in the CCA readings between the two tests indicates a bad ground connection. Diagnostic Tip: You also can use a digital voltmeter to check for voltage drop across all circuit connections, too. Ideally, you should see less than 0.1 volt drop across a good connection. More than 0.4 volts drop indicates high resistance and a dirty or loose connection. Diagnostic Tip: If the alternator on your car has failed, it might mean your battery is not building up normal resistance as it accepts a charge. This, in turn, makes the alternator keep charging the battery at a higher than normal rate. This can overload the charging system and lead to premature alternator failure. The battery charging output should jump about two volts after starting the engine (14.5 volts or higher), then gradually decrease after the engine has been running for several minutes (unless the battery is really low). The charging current should likewise taper off to less than 10 amps at idle (with no lights or accessories on) after five minutes of running. If a fully-charged battery is still pulling 20 or more amps after five minutes of idling, the battery is defective and needs to be replaced. How to Recharge A Battery Whether your battery tests GOOD or BAD, make sure the battery is fully recharged before returning it to service. The alternator is des…

Fonte: AA1Car.com