To determine if your car battery has sufficient power to start your engine in cold weather, you must assess its charge state using a voltmeter. An analog or digital voltmeter can be used, but a digital meter is recommended for its ease of reading and greater accuracy.
Before taking measurements, ensure the ignition key is turned off and all vehicle lights are switched off. To check the battery’s state of charge, connect the positive (red) voltmeter test lead to the battery’s positive terminal, typically marked with a plus symbol (+), and connected to a red cable. Connect the negative (black) voltmeter test to the battery’s negative terminal, typically marked with a minus symbol (-), and connected to a black cable.
Take note of the reading displayed on your voltmeter and consult the chart below.
Here is a table that shows the relationship between Battery Voltage and State of Charge at 80 degrees F. Please note that for every 10-degree F reduction in temperature, subtract 0.024 volts.
At the beginning of this page, there is a photo displaying a battery voltage reading of 12.29 volts. This reading indicates that the battery being tested is low and has only about half its charge. Therefore, the battery needs to be recharged.
Does Your Battery Have A Low Voltage Reading?
If your battery voltage reading is below 12.45 volts, indicating that it is only 75 percent charged, it is considered low and requires recharging. You can recharge your battery using a portable charger or drive your car for 15 to 20 minutes at 40 mph or faster.
Maintaining automotive lead-acid batteries at a charge level of 75 percent or higher is advisable for optimal performance and longevity. Suppose the battery can remain discharged for an extended period and is not recharged to 75 percent or higher within a few days. In that case, it may become permanently damaged due to sulfation. This process can hinder the cell plates inside the battery from accepting a full charge, ultimately reducing the battery’s performance and lifespan over time.
A Good Battery Is The Key to Starting Your Car in the Cold
During cold weather, a good battery becomes crucial for reliable engine startup as the low temperature increases the cranking load on the battery. When attempting to start a cold engine, the oil thickens at low temperatures, requiring more amps to crank the engine. For instance, at 0 degrees F, the number of cranking amps required to start a cold engine can increase up to twice as much. When the temperature drops to minus 15 degrees F or lower, it may require three times or more amps to start the engine, depending on the thickness of the oil present in the crankcase. As the oil gets thicker, it becomes more difficult to crank the engine.
In addition, cold temperatures harm the battery’s ability to supply amps. For example, at 0 degrees F, most batteries can only provide approximately 65% of their regular cranking amps. As the temperature drops to -20 degrees F, the battery’s power is reduced by half.
Warning: DO NOT attempt to recharge a battery that has run down and has frozen liquid inside, as doing so could cause the battery to explode. Removing the battery and bringing it indoors to thaw before recharging or testing it is crucial.
How Can You Determine If Your Battery Is Good Or Bad?
A battery that is considered to be in good condition can accept and hold a charge and produce an output of amperage close to its rated capacity. On the other hand, a battery in bad condition cannot accept or hold a charge or produce enough cranking amps. A good battery can be recharged and returned to service, while a bad one needs replacing.
The lifespan of most car batteries is about 4 to 5 years. However, in a late-model car that is not driven enough or far enough to keep the battery fully charged, the battery may only last 2 or 3 years. Additionally, hot climates can shorten battery life to 2 to 3 years.
If your battery is over four years old and is not holding a charge (drains quickly) or cannot start your engine at a normal speed, you likely need to purchase a new one.
Premature battery failure can occur due to chronic undercharging, regardless of the age of the battery. Car batteries are not designed for deep discharge, unlike marine or RV batteries. If a car battery is allowed to run down and is left in a discharged state for an extended period (such as a week or more), the plates may become sulfated and unable to accept a full charge when the battery is recharged. Over time, this will cause a decrease in battery capacity and eventual failure.
Undercharging can occur due to a faulty charging system (low charging voltage) or driving short distances during cold weather while simultaneously using the lights, heater, heated seats, defrosters, and radio. If the charging system cannot replace the amps used by your electrical system, your battery will gradually drain until it can no longer start your car.
Signs Of A Battery That Is Running Low:
When attempting to start, the engine cranks slowly or does not crank at all.
Abnormal electrical malfunctions include power windows not functioning properly, heated seats or electric defrosters not producing adequate heat, remote keyless entry failing to unlock doors or trunks, and more.
If your battery is low or dead, it does not necessarily mean it has failed or requires replacement. A healthy battery can lose its charge for various reasons. The cause can be:
- Always keep the lights on.
- Infrequent driving resulting in insufficient charging
- Prolonged vehicle inactivity
- Issues with the charging system or alternator
- Electrical problems that draw power from the battery while the car is turned off.
Therefore, it is important to test both the battery and charging system.
Testing Your Battery
Testing is the only way to determine whether your battery is in GOOD or BAD condition. Several auto parts stores offer free battery testing services. If the car is drivable, you can drive to a nearby auto parts store that provides free testing and have them examine your battery and charging system. If your car won’t start, remove the battery and ask a friend to drive you to the auto parts store for testing. While many repair shops also perform battery and charging system tests, they typically charge a fee for this service. However, some may offer free battery testing or deduct their diagnostic fee from the repair cost.
Warning: Handling traditional lead-acid car batteries, which use a mixture of water and sulfuric acid, with caution is important. Wear gloves to avoid any liquid spillage on your skin or clothing. Acid from the battery can lead to severe burns. In the event of a spill, rinse the affected area thoroughly with water and neutralize the acid using baking soda. It’s worth noting that AGM batteries do not contain liquid, so they are safer to handle and won’t spill.
There are primarily two methods of testing a battery. The traditional way involves using a Load Tester, which requires the battery to be recharged before conducting the test to obtain accurate results. The Load Tester applies a calibrated load to the battery, usually half its cold cranking amp [CCA] capacity or three times its amp/hour rating, and measures the battery voltage during the load test. If the voltage drops below 9.6 volts, the battery is deemed defective and needs replacement. However, if the voltage remains at or above 9.6 volts, the battery is considered functional and can be used again.
An alternative and faster approach to testing your battery are using an electronic “conductance” tester, such as the one demonstrated here. This device sends an alternating frequency signal through the battery to evaluate the condition of its cell plates. As the battery ages, its internal conductance decreases, while shorts, opens, and other cell defects also reduce conductance. Consequently, measuring conductance provides a precise assessment of battery health. The primary advantage of this method is that the battery does not require charging before testing, and most conductance testers can produce accurate results even if the battery is nearly depleted.
Furthermore, certain electronic battery testers can determine the battery’s CCA capacity, which helps determine the battery’s remaining service life. Additionally, some testers can measure the starter’s amperage when cranking the engine and analyze the charging system’s output under load once the engine is running. Sometimes, these testers even come with a built-in voltmeter to check connections.
Bad Battery Connections
If an electronic tester can determine the battery’s CCA rating, it can also be employed to diagnose poor ground connections. The CCA capacity is initially tested at the battery terminal connections, followed by testing at a ground point on the engine or elsewhere. A more than 25% difference in the CCA readings between the two tests indicates a problematic ground connection.
Diagnostic Tip: A digital voltmeter can measure the voltage drop across all circuit connections. The voltage drop should be less than 0.1 volts in a good connection. A voltage drop greater than 0.4 volts implies high resistance and a dirty or loose connection.
Diagnostic Tip: A failed alternator may cause the battery to charge higher than normal, preventing it from building up normal resistance while accepting a charge. This overload can damage the charging system and result in premature alternator failure. After starting the engine, the battery charging output should jump about two volts (14.5 volts or higher) and gradually decrease after several minutes of running (unless the battery is low). After five minutes of running, the charging current should also drop to less than ten amps at idle (without lights or accessories on). If a fully-charged battery still draws 20 or more amps after five minutes of idling, it is defective and requires replacement.
How to Recharge A Battery
Ensure that you fully recharge the battery, whether it tests GOOD or BAD, before returning it to service. Remember that the alternator is responsible for maintaining the battery charge, not recharging a dead battery. Charging a dead battery may overload the charging system and ultimately cause alternator damage.
The time required to recharge a battery depends on the battery’s charge level and the amp output of the charger used. The lower the battery voltage, the longer it will take to recharge. Similarly, a higher amp output charger will charge the battery more quickly.
For instance, a 40% charged battery with a voltage of about 12.2 volts may take approximately 20 to 40 minutes to reach full charge (12.6 volts) when charged with a 15 to 20 amp charger. A 10 amp charger will take twice as long (around 80 to 90 minutes), while a low-output 2 amp trickle charger may take overnight.
To recharge a battery, follow these basic steps:
- Turn OFF the ignition and anything else turned ON in the vehicle, such as lights or the radio.
- Locate the battery, which is usually under the hood. Still, it is possibly located in different locations, like inside the vehicle, under the back seat, inside the trunk, or behind an inner fender cover.
- Identify which battery post is POSITIVE and which is NEGATIVE. The positive post may have a + or POS symbol and/or a red cover, while the negative post may have a – or NEG symbol.
- Connect the BLACK NEGATIVE battery charger lead to the NEGATIVE post or clamp on the battery. Then, connect the RED POSITIVE charger lead to the POSITIVE post or clamp on the battery. It’s usually unimportant, leading you to attach first but ensure you don’t mix them up. Some chargers have built-in protections to prevent damage if the connections are accidentally reversed.
- Once the charger is connected to the battery, you can plug the charger into a 120-volt electrical outlet. Do NOT plug in the battery first because it may cause a spark when the connection is made, which could ignite hydrogen gas vented by the battery and cause an explosion.
- Leave the charger on until the battery is fully charged. Smart chargers will adjust the charging rate to fast charge the battery, while simple chargers or ones with adjustable charging rates will apply a constant charge that should decrease as the battery charges.
Check the battery voltage with a voltmeter to see if it’s fully charged. If not, keep charging the battery until it reaches full charge. If the battery still won’t charge after a long time, it may be BAD and must be replaced.
If the battery does not reach full charge after prolonged charging, it is likely defective and needs to be replaced. Slow charging can sometimes revive an old battery, but slow acceptance of a charge usually indicates the battery has died or reached the end of its life.
Caution: AVOID OVERCHARGING YOUR BATTERY! Suppose a battery is left on a continuous charger after it has been fully charged. In that case, it can overheat, potentially damaging the cells and causing excessive boiling and evaporating of the electrolyte inside the battery.
CAUTION: DO NOT TRY TO RECHARGE A BATTERY THAT IS FROZEN! Doing so may result in an explosion.
Variety Of Battery Chargers
There are different types of battery chargers that you can use to recharge your battery. Basic chargers range from simple and inexpensive “trickle” or maintenance chargers (2 amp output) to the general purpose 5 to 15 amp units widely available in various retail outlets. “Smart” chargers have built-in electronics that automatically adjust the charging rate and voltage, providing faster charging and less risk of over-charging or battery damage. Some Smart Chargers can even detect the battery voltage (6V or 12V) and the type of battery (wet cell, AGM, or gel cell), adjusting their output and charging rate accordingly.
A smart charger generally follows a three-stage charging process. The initial stage is known as the “bulk” stage, which supplies the battery with maximum voltage (14.4 to 14.7 volts for a 12V car battery) and maximum amperage to quickly charge the battery up to 80 percent of its capacity. The next stage is the “absorption” stage, where the charging amperage is reduced while the output voltage remains constant. This stage takes longer due to increased resistance inside the battery as it nears full charge. Once the battery reaches approximately 90 to 95 percent of its full charge, the charger enters the “float” stage and maintains a constant charging voltage at a minimum current. Some chargers will also automatically shut off once the battery is fully charged.
Caution: To prevent damage to the battery, refrain from overcharging it. If a battery is continuously charged after it has been fully charged, it may result in cell damage or lead to excessive boiling and evaporation of the electrolyte.
Caution: There is a risk of explosion if you try to recharge a battery that has been frozen. Please do not attempt to recharge it.
How To Check The Charging System
Attach a digital voltmeter to the positive (+) and negative (-) battery terminals to check if your charging system is working, and then start your engine. If the charging system functions correctly, the voltage reading will rise to 13.5 to 14.5 volts.
If the voltage reading remains unchanged, this indicates a malfunction in the charging system, failing to charge the battery. In such cases, you may need to replace the alternator. To determine whether the alternator is faulty, take it to an auto parts store and have it tested on a specialized machine that measures the unit’s current and voltage outputs. If the alternator tests as defective, you will need to replace it. However, if the alternator tests as functional, the issue lies elsewhere in the charging system, such as a faulty wiring connection or a problem with the engine’s computer, which regulates the charging voltage.
Replacement Car Batteries
Before purchasing a replacement battery, it is important to ensure it has the same post configuration as the original battery (either top post or side post) and fits properly in the battery tray. Your first task, therefore, is to determine the appropriate “Group Size” for your vehicle.
Once you have determined the correct Group Size, the next step is to identify the number of Cold Cranking Amps (CCAs) required for reliable cold weather starting. The replacement battery should have a CCA rating equal to or greater than the original battery. In colder climates, larger CCA ratings are typically preferable. However, it is important to note that some batteries may sacrifice their “reserve capacity” to achieve higher CCA ratings.
Another crucial factor to consider is the number of months of prorated warranty coverage the battery manufacturer offers. Generally, batteries with higher warranty periods are associated with higher CCA ratings and superior quality. As such, upgrading from a basic 24-month replacement battery to a premium battery with an extended warranty period of 36 months or more is worth upgrading. A warranty usually includes free replacement if the battery fails within the first two years, followed by a prorated credit if it fails during the remainder of the warranty period.
Additionally, there are variations in battery technology and design. Although all automotive batteries currently use lead-acid chemistry, advancements such as redesigned grids, thinner plates, and new connectors have allowed for higher amperage to be accommodated in smaller cases. Some batteries adopt a “spiral wound” cell configuration instead of flat plates, which increases packaging density, power output, and durability. Absorbent Glass Mat (AGM) batteries do not contain liquid because their electrolyte is a paste between the cell plates. These batteries are spill-proof, more resilient to vibration damage, and typically last a year or two longer than conventional wet-cell batteries. AGM batteries are frequently found in newer vehicles with fuel-saving idle stop-start systems.
Some batteries use a “gel” electrolyte or “recombination” technology instead of liquid acid. Additionally, some batteries feature “absorbed glass mat” (AGM) separators between the plates, which hold the acid like a paper towel absorbs water. This design makes the battery spill-proof even in the event of a puncture. AGM technology also enhances the battery’s ability to withstand vibration damage and prolongs its service life.
Car Battery Ratings
Knowing battery ratings is essential to testing or replacing your car battery.
Cold Cranking Amps (CCA)
The most commonly used battery capacity rating is the Cold Cranking Amps (CCA). It represents the number of amps a battery can provide for 30 seconds at 0 degrees Fahrenheit while maintaining a post voltage of 7.2 Volts. Most vehicles require 400 to 600 cold cranking amps to ensure dependable cold weather starting, and engines with higher displacement require even more cranking amps. While some batteries have a rating of up to 1000 CCA, they may trade off reserve capacity to obtain high short-term outputs.
Cranking Amps (CA)
This rating is of lesser significance and is measured at 32 degrees Fahrenheit. It is the same as CCA, except for the temperature difference. You can convert a battery’s CA rating to CCA by dividing the number by 1.28. For instance, a battery with a CA rating of 500 amps would become 390 CCA after conversion.
Reserve Capacity (RC)
Consider this as the battery’s endurance capability. It refers to the duration in minutes that the battery can deliver 25 amps while maintaining a post voltage of 10.5 volts. A higher reserve capacity rating indicates that the battery can last longer if the charging system malfunctions. Most car batteries have a reserve capacity rating ranging from 90 to 120. A higher rating implies a better battery.
Amp Hour Rating (A/H)
This rating has become less common in use. It evaluates the battery’s ability to sustain a low current draw for 20 hours while maintaining a minimum voltage of 10.5 Volts at 70 degrees F. For instance, a drain of 3 amps for 20 hours would give a 60 A/H rating.
Installing New Battery
Before installing a new battery, inspect and clean the battery posts and cables and check the negative battery cable’s ground connection and engine ground straps for any signs of damage or corrosion. Any loose or corroded connections can lead to charging and starting issues.