But a positive outcome of the tests outlined above should prove the battery itself can hold a charge. Even an errant radio or internal light connection can repeatedly flatten a good one. It could be good and several scenarios might lead it to lose its charge: such as lights being left on, undriven for long periods, dodgy alternator, or even parasitic draw through any number of electrical circuits in the car going awry. Of course, a repeatedly low charge doesn’t mean your battery is dead. They are built to maintain charge as opposed to keeping dead ones alive. Also, avoid running a known bad battery as you could end up ruining the alternator. This is where smart units are advantageous, preventing damage and thus extra cost. Once they reach full charge, it is time to unplug the charger. There is also less chance of overcharging and they can detect whether the batter is 6V or 12V, as well as the type (such as wet or gel cell) and adjust the output accordingly.ĬAUTION: car batteries should never be overcharged. So-called smart chargers adjust their voltage output depending on the status of the battery and can charge faster and more efficiently. There are different types of automotive battery chargers, from basic 2A trickle chargers to more expensive 10A general purpose devices. WARNING: if you remove it, note that battery acid burns when in contact with the skin so handle with care. Alternatively, repair shops may also offer a free test, plus the cost of potential repair. Some auto parts garages can perform these test for free, either by driving there or taking the battery in. The high voltage will likely be in the 14V area and is perfectly normal, while a drop under 9.6V during the process would indicate it can no longer effectively hold charge and needs changing.Įlectronic test: checks the battery cells via a frequency test. This will automatically store the high and low voltages it picks up. You can do this by starting the engine and monitoring the voltage with a multimeter that has a Min/Max mode. Load test: a load is applied to the battery while its voltage is monitored. When fully charged, the battery can be tested further using a couple of methods: If not, consider getting it checked out fully prior to a replacement. Another option is to get the battery charged at your local auto parts store.Īfter charging, perform the same test as above to see if the battery now registers in the 12.6V range. Note: it is not enough to just start the engine and let it sit you want it working under load to receive a proper charge from the alternator. The other option is to drive the car for around 30 minutes. You can do this with a portable charger plugged into the mains, which will apply gradual current and take time. If after recharging it doesn’t hold the charge, then it is probably on its way out. It does not, however, indicate that it is bad. Note the DC volts reading and compare with the table below, which indicates charge, under no-load, status:Ĭar batteries provide 12.6V DC (direct current) through six cells, producing 2.1V each.Īnything under the 75% charge rate, or about 12.45V, generally indicates the battery is undercharged and will need recharging. The meter is now connected in parallel with the car battery and will display a reading automatically. With the red lead plugged into the voltage (main) terminal of the multimeter and the black lead plugged into the common (COM) terminal of the multimeter: position the red lead onto the positive (+, usually red) terminal of the battery and the black lead to the negative (–, usually black) terminal. The 20V range means it will measure between 0V and 20V. Most of the manual ranging meters have a 20V range, which is what you would need to test a car battery. The wavy line after a V is AC (alternating current) voltage and is for checking the mains voltage in your house. DC voltage is usually marked as a V followed by a short line with a dotted line beneath it. Select the DC volts position on your multimeter (or the 12V setting if you have a dedicated car battery test range). If you don’t know how to use a multimeter to test a car battery, read the procedure below:Įnsure the ignition, lights and radio are off. And even a cheap, category I (CAT-I) multimeter is fine as you are merely testing voltage, not amperage. Digital multimeters are the best option for this since they give a more accurate reading, although you could also use an analog one. Other than trying to start the engine to see if there’s charge, the best way to decipher a car battery’s status is to test it using a multimeter. If you are looking to test for amperage draw (parasitic draw) – testing amps in series – we cover that process in this guide. This is achieved by measuring the DC voltage of the battery in parallel with the multimeter. Here, we check the charge, or voltage, of your car battery.
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