How many volts should a alternator kick out?

Most modern car alternators regulate their output to about 13.8 to 14.4 volts while the engine is running, with roughly 14.0 to 14.4 volts as the typical target during charging.

Understanding why this matters helps protect the battery and electronics. The exact voltage can vary by vehicle, regulator design, temperature, and electrical load, but a regulated output around 14 volts is the standard goal for effective charging without overcharging. In some scenarios—such as very cold starts or high electrical demand—a short-lived higher reading is possible, while sustained voltages above 15 V generally indicate a fault.

Typical charging voltage targets

To give you a sense of the ranges you might see, manufacturers and service manuals describe a broad band rather than a single fixed value.

• 13.5–13.8 volts when the engine is running with light load or near battery full state.


• 14.0–14.4 volts during normal charging with typical electrical demand.


• Up to about 14.6–14.8 volts in some systems under high load or when the battery is heavily discharged (short-term).

These figures reflect typical automotive regulators. They balance the need to replenish the battery and power the vehicle’s electronics without causing premature battery wear or electrical stress.

How to measure the alternator’s output

Reliable verification starts with a simple voltage check at the battery with the engine running and under load. The steps below outline a practical approach for most drivers.

1. With the engine off and the battery rested, set your digital multimeter to DC volts and measure across the battery terminals; a healthy 12-volt battery should read about 12.6 volts.


2. Start the engine and let it settle to idle, then re-check the battery terminals; you should see about 13.8–14.4 volts as the alternator engages.


3. Turn on electrical loads (headlights, A/C, fans) to simulate driving conditions; voltages should stay within roughly 13.5–14.8 volts.


4. If the reading remains consistently outside this range, especially above 15 volts or below 13.0 volts, have the charging system inspected by a professional.

Remember that battery health, wiring quality, and grounding influence readings. If in doubt, have a technician perform a full regulator and alternator test.

What to do if the alternator is out of spec

Voltage too low (under about 13.5 V when running)

Causes include a failing regulator, slipping belt, poor connections, corroded terminals, or a weak battery. Consequences can include insufficient charging, a shortfall for electronics, and a shortened battery life.

Voltage too high (over about 14.8 V when running)

Overcharging can damage the battery and sensitive electronics and may point to a faulty regulator or alternator. If you see sustained high voltage, reduce electrical load and seek diagnostic service promptly.

In any case, a professional diagnostic that includes a load test and regulator check is recommended if readings stay outside the described ranges for an extended period.

Summary

The charging voltage for most passenger cars sits around 14 volts, with an acceptable range roughly from 13.5 to 14.8 volts depending on load and vehicle design. Regular checks help protect the battery and electrical system, and a stable reading within the recommended bands is a sign of a healthy charging system.

How to test alternator output voltage?

To test an alternator's output voltage, first use a multimeter to check the battery voltage with the engine off, which should be around 12.612.612.6 volts. Then, start the engine and measure the voltage again; it should rise to between 14.214.214.2 and 14.714.714.7 volts. To test under load, turn on accessories like headlights, and the voltage should stay above 131313 volts. 
This video demonstrates how to test your alternator with a multimeter: 1mClassic Car MaintenanceYouTube · Apr 1, 2024
Step 1: Test with the engine off 

• Set your multimeter to DC volts and select a range of at least $20$V. 
• Connect the red probe to the positive (+) battery terminal and the black probe to the negative (-) terminal. 
• Read the voltage. A fully charged battery should show about $12.6$V. If it's lower, charge the battery before proceeding. 

Step 2: Test with the engine running 

• With the multimeter still connected, start the engine. 
• The voltage should rise to between 14.214.214.2 and $14.7$V, indicating the alternator is charging the battery. 

This video shows how to test an alternator when the engine is running: 59sChrisFixYouTube · May 14, 2014
Step 3: Test under load 

• Keep the engine running and turn on the headlights, radio, and other accessories.
• The voltage may drop slightly but should not go below $13$V and should return to the charging range after a moment. 

What the results mean

• Voltage remains below $13$V with the engine on: This could indicate a weak alternator or a problem with the connections or belt. 
• Voltage is consistently above $14.7$V: The alternator is overcharging the battery, which can cause damage. 
• Voltage does not increase from the off-engine reading: This suggests a non-functional alternator. 
• Voltage drops below $12.7$V with accessories on: This can signal a faulty alternator or a loose connection. 

How many volts should my alternator be pushing out?

A car alternator should put out between 13.5 and 14.5 volts while the engine is running to charge the battery, though the exact voltage can fluctuate with electrical load and engine speed. A steady reading, even with accessories like lights and the radio on, indicates it's working correctly. Readings consistently below 13 volts or above 15 volts can signal a problem. 
Normal operating voltage

• Engine running (low load): Approximately 13.5 to 14.5 volts. 
• Engine running (high load): The voltage may drop to around 13 volts, but should remain above that while the alternator is functioning correctly. 
• Optimal range: Many sources cite a "sweet spot" of around 14.2 to 14.4 volts. 

When to be concerned

• Voltage is consistently below 13 volts: This indicates the alternator isn't charging the battery properly, and the battery may be draining. 
• Voltage is consistently above 15 volts: This can mean the voltage regulator is failing and overcharging the battery, which can cause damage. 

How to test

1. Start your car and turn off all accessories like lights, radio, and the heater. 
2. Place the positive and negative probes of a multimeter on the battery terminals. 
3. Read the voltage. It should be between 13.5 and 14.5 volts. 
4. Turn on all accessories (headlights, heater, wipers, radio). 
5. Check the voltage again. It may drop slightly but should still be at least 13 volts. 

What is a good alternator puts out within?

A good car alternator puts out between 13.5 and 14.5 volts with the engine running and accessories off. At idle, the voltage should be around 13.513.513.5 volts, and while driving, it may rise slightly but should remain below 151515 volts. A reading outside of this range can indicate a problem with the alternator or battery. 

• Normal operating range: The ideal voltage for a car alternator is typically between 13.513.513.5 and 14.514.514.5 volts. 
• At idle: Expect a reading of about 13.513.513.5 volts. 
• While driving: The voltage may increase, but it should stay below 151515 volts. 
• Signs of a problem:
  • Low voltage: (less than 131313 volts) could indicate a bad alternator or battery. 
  • High voltage: (over 14.714.714.7 volts and climbing) can signal an overcharging problem caused by a bad voltage regulator. 
  • Fluctuating voltage: can also point to an issue. 

Is 13V good for an alternator?

13+ is good, once driving you'll probably see over 14 volts. Alternators are smart these days and don't need to produce 14+ volts when both batteries are fully charged. Usually see 13 when the battery is charged and 14 when it is being charged like right after you start it.