How to Choose Car 12V Battery Testers or Meters
Automotive Battery Health Monitors and Voltmeters
Oct 11, 2009
While voltmeters are already built into the dashboard of some cars, others may only have a "change battery" warning "idiot light" that doesn't provide much information.
Measuring a car battery's voltage is simple. Any driver can do it. Some battery testers just plug into the cigarette lighter socket. They give useful information about the health of the battery and alternator (charging system). This provides peace of mind. The driver can be confident that his battery isn't going to go flat and leave him stranded. This means that even old or reconditioned batteries can be used with confidence.
If a car does fail to start, the tester can be used to check whether or not battery failure is the cause.
Running a car stereo at a tailgating party (and other uses of the vehicle's battery power with the engine off) will drain the battery. A voltage tester can be used to check the battery's condition, helping to decide whether to switch off the stereo or to continue the party.
Voltage testers range from simple $10 consumer models to professional models costing a few hundred dollars.
Understanding Car Battery Voltages
There are three important voltages to measure:
- Battery no-load voltage. This is the voltage of the battery when the engine is off and no electrical devices are running (radio, headlamps). It should be 12 volts for most cars.
- Cranking or starting voltage: the battery's voltage when starting the engine. This is a key measure of battery health. The battery's voltage will drop when the engine is cranked. As the battery ages, the voltage drops more and more. If the voltage is too low, the battery will be too weak to start the engine.
- Charging or alternator voltage. This is the voltage measured with the engine running. It should be a few volts higher than the no-load voltage. A low voltage means that the battery isn't being charged by the alternator: time to visit the mechanic before the battery goes flat.
A battery tester should be able to measure all three voltages. Cheaper digital testers can't measure the cranking voltage.
Types of Car Battery Voltage Testers and Voltmeters
Testers that plug into the cigarette lighter socket are the easiest to use. No installation is required. They can be analog or digital. Most are "self-powered", running off the car battery's power. A separate battery is not needed. Many testers of this type are cheap and flimsy. Because they stick out from the dashboard, they are often accidentally knocked off and broken if left plugged in.
Other testers are clamped directly to the battery terminals. They can only be used when the car is stationary and the hood is up. Some can be left permanently clamped to the battery with the display inside the engine compartment.
Some clamp-on testers are designed to be used with standalone batteries that have been removed from the car. To measure cranking voltage, they have their own load tester capable of absorbing 100 or more amperes.
Most convenient are voltmeters that are permanently fixed to the car dashboard. They allow the voltage to be easily monitored every day. However some installation work is required, and they can't be shared with another car.
Analog Versus Digital Voltage Testers
Digital displays may look more precise but they aren't necessarily more accurate. Some have numeric displays that show the voltage to the nearest tenth (0.1) of a volt. Others only indicate the battery's condition with a few LED lights.
One advantage of a traditional swinging needle analog meter is that the cranking voltage can be seen (though the needle may vibrate crazily, making it difficult to get an accurate reading). Cheaper digital meters will blank out when the engine is cranked.
The Best Car Battery Voltage Tester
A car battery tester should ideally measure no-load, cranking and charging voltages. However a tester that only measures no-load and charging voltages is obviously better than no tester. The mounting type (cigarette lighter, dashboard, engine compartment) and whether digital or analog, is not critical and is a matter of individual preference.
There are many generic brands of consumer battery testers available. Brands of professional testers used by mechanics include Midtronics and Associated Equipment.
Besides checking the battery with a battery tester, drivers should know how to troubleshoot car-starting problems and jump start a car. A portable jump starter is also a good investment.
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