3 reasons to stop checking your car’s battery with a multimeter
Car batteries always die at the worst time. It’s never on a warm, lazy Sunday afternoon when you have nothing better to do then get on the phone with AAA.
No, car batteries die on freezing cold Monday mornings when you’re already running late for work. Right? You spilled coffee all over your shirt, you’re shivering in the car, and you hear that dreadful sound – or lack thereof – as you turn the keys in the ignition. You instantly know: your car’s battery is dead.
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Maybe your tools are in the back of your truck, so you’re tempted to check the car battery with a multimeter. I mean you have one, why not? Well, testing a car battery with a standard multimeter may give you false results. Even a battery with poor capacity can measure the proper voltage on a multimeter.
Read on to learn the three biggest reasons why you shouldn’t use a multimeter to check your car’s battery.
Batteries consist of positive and negative plates submerged in a liquid electrolyte. Where the electrolyte meets the plate, a boundary is formed. This boundary will have 2 layers of charge with opposing polarities; 1 at the surface of the plate, and 1 in the electrolyte. These layers will be separated by a single layer of molecules that adhere to the surface of the electrode and act like a dielectric. This forms what is known as double-layer capacitance. The amount of charge stored in this double-layer will depend on the applied voltage. So even a battery with little to no capacity can still hold a charge.
A digital multimeter is a high impedance device, so the impedance between the positive lead and negative lead will generally be 10 Megohms or higher. This places virtually no load on the battery. Even a battery with little to no capacity will read the proper voltage.
3. Better options available
In order to properly measure a battery, our experts suggest that you use a meter with a lower input impedance. These are typically in the form of a battery tester. These testers will place a load across the battery and then measure the voltage, which is way more trustworthy than a standard digital multimeter. Plus, you’ll avoid those potential false positives that we talked about.
In this blog, we’re talking specifically about car batteries, but the same applies to all batteries. We – of course – don’t recommend using a digital multimeter to check your batteries, but we do recommend our battery testing equipment. To view the full range of test equipment, click here.
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