Battery cables should be checked every 3 months or 3,000 miles. In most cases you can easily see the battery when you're looking under the hood. The front corner of the engine compartment is a common location to find the battery, but on some vehicles it may be in the trunk or under the backseat. Keep in mind that diesel trucks may have two batteries instead of one.
Checking the Condition of the Battery
Special battery testers are used to check the electrical condition of battery, which you can have done at a service center or parts store. However, you can check of the physical condition of the battery yourself with just a visual inspection. Have the battery replaced if it:
Is bulging out on any of the sides
Is damaged in any way
Even if a battery appears to be in good physical condition, have it checked by a professional if you begin to have starting issues.
A clean battery in good condition, with a properly installed hold-down.
A corroded and leaking battery in poor condition.
Battery Terminal Condition
A good connection between the battery cables and the battery terminals is crucial for proper operation of electrical systems. When looking at the battery terminals, check for corrosion and make sure that the connections are not loose.
A loose battery cable can cause starting problems, even if the battery itself and the starter motor are OK. If you're having issues starting your car, double check that all the connections are clean and tight.
Over time, having loose battery cables could potentially lead to alternator failure.
When tightening battery cables, be sure to use the right size wrench or socket so you don't strip or round off out the fastener. Also, battery terminals and cable ends are often made of lead – so be sure to wash your hands when you are done.
Despite the name, a 12 volt battery is actually 12.6 volts if fully charged. A battery's voltage can be used as an indicator of how charged the battery is.
Voltage State of charge*
*Note that these readings are for a battery at 80°F. As temperature drops, these values will go down slightly.
How to Check Battery Voltage
Battery voltage is checked with a voltmeter or digital multimeter (also called a digital volt/ohm meter – DVOM). Although battery testers are somewhat expensive, you can purchase a digital voltmeter fairly reasonable at a hardware or tool store. Read the instructions for how to use the particular voltmeter you buy. To check battery voltage:
Have the ignition key and all electrical accessories OFF.
Turn the voltmeter on and set it to DC voltage (the icon that looks like a V with a straight line above it).
Touch the voltmeter's negative lead (the black one) to the battery's negative terminal and the voltmeter's positive lead (the red one) to the battery's positive cable.
Read the voltage on the screen.
To check the charging system voltage, do the exact same thing but have the engine running. Be mindful of fans, belts, and other moving parts as you do this.
When the ignition is off, battery voltage should be around 12.4 to 12.6 volts. When the engine is running, the voltage should be about 13.5 to 14.5 volts because the vehicle's alternator is generating electricity and charging the battery.
Keep in mind that a voltmeter is not the same thing as a battery tester. While a battery tester actually checks the electrical condition of the battery, a voltmeter merely shows the battery's voltage. Just because a battery is fully charged doesn't necessarily mean it's good.
Battery Hold Down
A battery's hold down is important to keep the battery secure and in place. Excess vibration can damage the battery and thus shorten its life. If the battery moves too far the terminals can short out on metal components, which can lead to electrical arcing, sparks, a fire, or an explosion. Also, if the battery tips over it could leak acid in the engine compartment or come into contact with moving parts such as the fan or drive belt. Because of this, when looking at the battery be sure that the hold down is in good condition and properly tightened.
Most automotive batteries have a liquid electrolyte inside that is 75% water and 25% sulfuric acid. As a battery's state of charge goes down, the temperature at which it can freeze goes up. While a fully charged battery won't freeze until about -75°F, a completely dead one (anything less than 12 volts) can freeze at about the same temperature as water – at 32°F. If a battery's charge runs too low and it freezes, it will likely need to be replaced. Some things to check if you think your battery might be frozen include:
Frost present on the battery itself.
Bulges, cracks, or distortion in the case.
No sound of liquid sloshing around inside the battery when moving it.
Do NOT try to jump start or charge a frozen battery, as it could explode.
Get Your Vehicle Serviced if You Notice:
A leaking or damaged battery
A missing battery hold down
Starting or charging problems
The red charging indicator light comes on
You suspect a frozen battery