The problem should be corrected and the battery replaced. ![]() Check for cloudy or discoloured electrolyte caused by overcharging or vibration.When water is added, always charge the battery to make sure the water and acid mix. If necessary, add distilled water to each low cell. The proper level is just below the vent funnel. The level can be viewed through the translucent plastic case or by removing the vent caps and looking directly into each cell. Check for a loose battery hold-down and loose cable connections.A wire brush is needed for heavy corrosion on the terminals. Clean the terminals and case top with a mixture of water and baking soda. Check for corrosion on terminals and dirt or acid on the case top.Check for cracked or broken cables or connections.Check for cracks in the battery case and for broken terminals.However knowing a cell is 'dead' is of no more use to you than knowing that the battery won't hold a charge, so a test of the resting voltage is just as effective a diagnosis. You can buy a hydrometer-style battery tester that measures the specific gravity of the battery acid, and can tell you whether any cells are 'dead' or not. The cells contain a mix of water and sulphuric acid, so you don't really want to be messing around inside them too much. The cells will either have individual caps, or a plastic cover that clips over all, or some of the cells. But some older batteries allow you to access the individual cells. Many new car batteries are of the sealed 'maintenance-free variety. TOP TIP: Before you disconnect your battery make sure you know the code for your stereo – otherwise you may find it won't work when you reconnect it! How do I test a car battery for dead cells? If the battery holds a charge when it's not connected to the car, it's not faulty. Then, fully charge the battery, leave it for 12 hours and test it. Apart from doing the obvious (setting your phone to record video before you place it in the boot or glovebox to see if the bulb is staying on), you can either remove the leads from the battery, or remove it from the car entirely. This is where something electrical - a light or a motor for example - is draining the battery, even with the engine turned off. If the battery is continually going flat, it could be because of a 'parasitic loss'. What do I do if the car battery is repeatedly going flat? Bear in mind that when a battery goes down to 12.2V it's actually only 50% charged, and below 12V it's classed as discharged. The resting voltage should ideally be no lower than 12.6V. ![]() If you're getting a reading with a minus in front of it (-12.6 rather than 12.6) you've got the probes the wrong way round. The terminals will be marked '+' and '-'. Hold the red probe to the positive terminal and the black probe to the negative terminal. This will allow you to accurately measure 0-20 volts. Using your multimeter, you want to measure DC voltage (this is indicated with a solid line and a dashed line above a letter V). Once the car battery is exposed be careful that nothing metal touches the terminals, so don't rest any spanners or other tools on it. Haynes manuals show you where to find your battery and make the job of replacing it easy by guiding you step-by-step. There may also be a cover over the positive (+) terminal, which usually lifts off. The first thing to do is make sure you can access the two terminals on the top of the car battery.Ĭar batteries are commonly located in the engine bay to one side of the engine, and often have a plastic cover which will unclip, lift off, or occasionally require the removal of a couple of bolts. Testing a car battery with a multimeter is a simple process. ![]() How do I use a multimeter to test a car battery? Discover which Haynes Manual is best for you.NEW Fault Finder - Diagnose the problem.
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