Key takeaways
Set the multimeter to 20 volts DC, touch red to the positive terminal and black to the negative, and read the battery after it has rested for at least an hour. A flooded battery at 12.6 volts or higher is fully charged, one at 11.9 volts or lower is dead, and the reading should rise to about 13.7 to 14.7 volts with the engine running.
- 01While the engine cranks, a healthy battery holds above about 10 volts. Load-test pass lines drop in the cold, to 8.5 volts at 0°F.
- 02AGM batteries read higher when full than flooded ones, so an AGM at 12.6 volts is only about three-quarters charged.
- 03Smart charging systems, such as Honda's, can run as low as 12.5 volts on purpose, so check the alternator with the headlights and blower on.
- 04Voltage shows charge, not health. A battery that reads well but cranks weakly still needs a proper battery test, which AutoZone offers free at its U.S. stores.
This guide belongs to our Car maintenance guide: battery and electrical section, which covers the wider topic.
A multimeter answers the two questions that matter when a car is slow to start: is the battery charged, and is the alternator keeping it charged? Set the meter to 20 volts DC, touch the red probe to the positive (+) terminal and the black probe to the negative (−), and take three readings: engine off, while it cranks and while it runs.
A rested, fully charged battery should read 12.6 volts or higher, and one at 11.9 volts or lower is considered dead, according to Interstate Batteries' support FAQs. With the engine running, Interstate expects 13.7 to 14.7 volts.
This guide covers 12-volt cars, SUVs and pickups with flooded, EFB or AGM batteries, including how temperature and smart charging change the numbers. For battery life spans and warning signs, see the Battery & Electrical section of our car maintenance guide.
Battery Voltage Readings at a Glance
Healthy numbers are 12.6 volts or more at rest, above 10 volts while cranking, 13.7 to 14.7 volts with the engine running and under 50 milliamps of draw once the car is asleep.
| Test | Engine | Healthy reading | Problem reading |
|---|---|---|---|
| Resting voltage | Off, rested at least 1 hour | 12.6 volts or higher | 11.9 volts or lower means dead |
| Cranking voltage | Starting | Stays above 10 volts | Below 10 volts |
| Charging voltage | Running at idle | 13.7 to 14.7 volts | Below 13 volts |
| Parasitic draw | Off, modules asleep | Under 50 milliamps | Over 100 milliamps |
Resting and charging figures from Interstate Batteries. Cranking figures from J.D. Power. Draw limits from Fluke. Rest time from Haynes and AutoZone.
What You Need Before You Test
You need a digital multimeter, eye and hand protection, and an hour of rest for the battery if the car was just driven.
- A digital multimeter with DC volts and, for draw tests, a 10A jack
- Clip-on test leads for the draw test
- Safety glasses and nitrile or rubber gloves
- Fine-grit sandpaper or a wire brush for corroded terminals
- A helper for the cranking test
- Your owner's manual, to find the battery
J.D. Power's battery test guide says to scrub corrosion off the terminals with fine-grit sandpaper before you measure. AutoZone calls for gloves and eye protection whenever you remove battery caps.
Digital or analog multimeter?
Pick a digital meter. Battery thresholds sit only tenths of a volt apart, and a digital screen shows them directly.
| Feature | Digital multimeter | Analog multimeter |
|---|---|---|
| Display | Numbers on a screen | Needle over a printed scale |
| Accuracy | High, with direct readings | Lower, partly from parallax error |
| Input impedance | High and usually constant | Lower, and it changes with the range |
| Range selection | Manual or automatic | Manual |
| Strong point | Exact readings, such as 12.45 volts | Showing a value that swings |
Comparison from Schneider Electric's analog vs. digital multimeter guide.
Schneider Electric's meter comparison notes that an analog needle can mislead if you don't view it straight on. Its moving pointer does make a rising or falling voltage easier to watch.
Which multimeter setting to use
Use DC volts on the 20-volt range. Haynes' multimeter guide says the DC volts setting is marked by a solid line and a dashed line above the V, and the 20 setting reads from 0 to 20 volts.
If your meter has no numbered ranges, AutoZone says to simply set it to DC volts. Plug the black lead into COM and the red lead into the jack marked V or VΩ, as Fluke's battery voltage guide shows.
A lone 1 on the screen usually means the range is too low, according to SparkFun's multimeter tutorial. A minus sign, as in -12.6, only means the probes are reversed.
Time, Difficulty and Safety
The voltage checks are beginner work once the battery has rested. The draw and cable tests take longer and need more care.
| Step | Difficulty | Time |
|---|---|---|
| Let the battery rest | Easy | At least 1 hour, ideally overnight |
| Remove surface charge (optional) | Easy | Headlights on for about 1 to 2 minutes |
| Cranking test | Easy | One start, cranking 10 seconds or less |
| Parasitic draw test | Intermediate | 10 to 45 minutes for modules to sleep |
| Cable voltage drop test | Intermediate | 4 to 5 seconds of cranking per side |
Times from Haynes, AutoZone, Fluke, J.D. Power and the 2022 Ram 2500/3500 owner's manual. Difficulty ratings are CarTipsMentor's.
A 12-volt battery still deserves respect. Fluke warns that lead-acid batteries can give off explosive gas and contain acid.
- Wear glasses and gloves, and keep sparks and flames away.
- Never let a probe, wrench or watch band bridge both terminals. Haynes says not to rest tools on the battery.
- Keep hands, hair and leads clear of the fan and belts whenever the engine runs.
Don't test a swollen or leaking battery
A bulging case, leaking acid or a rotten-egg smell means the battery is damaged. Don't put probes or clamps on it. Keep people away and call a tow or a mobile battery service.
AAA's battery vs. alternator guide says a rotten-egg smell comes from overheated battery acid turning into hydrogen gas. If the case has swollen, AAA says not to touch it and to call a tow truck.
The Multimeter Battery Test, Step by Step
Work through the checks in this order: resting voltage, cranking voltage, then charging voltage. If your owner's manual gives different specs, follow the manual.
- Park and wait. Set the parking brake, turn the ignition off and let the car sit at least an hour. Haynes says an overnight rest and a morning test give a really accurate gauge of the state of charge.
- Switch off every load. Lights, radio and climate control go off, and the key comes out.
- Find and clean the terminals. The positive post is marked + and often has a red cover. The negative is marked −.
- Short on time? Bleed off surface charge. If the car was just driven, run the headlights for about a minute, then switch them off.
- Set the meter. Black lead in COM, red lead in V, dial on DC volts at the 20 range.
- Touch red to positive and black to negative. Press each tip onto bare metal and hold it steady.
- Record the resting voltage. On a flooded battery, 12.6 volts or more means full. Check other types against the chart below.
- Watch the meter while a helper starts the engine. Note the lowest number. A MIN/MAX button, if your meter has one, records the dip for you. Stop cranking after 10 seconds.
- Read the charging voltage at idle. Most sources expect about 13.7 to 14.7 volts.
- Repeat with the loads on. Turn on the headlights and the heater blower. The reading should stay at 13.5 volts or higher.
- Shut down and log it. Remove the probes and write down all three readings with the date.
Battery in the trunk or under a seat?
Measure at the battery's own terminals, not at the jump-start posts under the hood. VARTA says the resistance of the vehicle's cabling affects readings taken at those remote points.
How Long Should a Battery Rest Before You Test It?
At least an hour, and overnight is better. Driving or charging leaves a surface charge that can make a battery read higher than its true state of charge.
AutoZone's multimeter guide says to test only after the battery has sat unused for at least an hour, because testing right after use can give a false reading.
Battery makers set a stricter bar. Discover Battery's charge guide says the true open-circuit voltage can only be measured after 24 hours off charge or load. After a wall charge, AAA suggests letting the battery sit two days before you test it.
When you can't wait, use the headlights. Fluke suggests about one minute and J.D. Power about two.
What Your Resting Voltage Means
Resting voltage shows state of charge. About 12.6 volts is full for a flooded battery and about 12.8 volts for an AGM, and under 11.8 volts is empty for both.
| State of charge | Flooded | AGM | Gel |
|---|---|---|---|
| 100% | Above 12.60 V | Above 12.80 V | Above 12.85 V |
| 75% | Above 12.40 V | Above 12.60 V | Above 12.65 V |
| 50% | Above 12.20 V | Above 12.30 V | Above 12.35 V |
| 25% | Above 12.00 V | Above 12.00 V | Above 12.00 V |
| 0% | Below 11.80 V | Below 11.80 V | Below 11.80 V |
Open-circuit voltages for 12-volt batteries at rest, from Discover Battery.
Fluke's figures match the flooded column, with about 12.6 volts at full charge and about 12.2 at 50 percent. VARTA's battery testing guide calls about 12.8 volts ideal for a conventional battery and says to recharge one below 12.4 volts as soon as possible.
AutoZone suggests a full charge and a retest for anything from 12.3 to 12.5 volts. If the battery reads 11.9 volts or lower and you need the car today, our guide on how to jump start a car safely covers the clamp order. AutoZone advises against jumping a battery at 8 volts or below, because of the strain it puts on the alternator.
AGM, EFB and flooded batteries read differently
Check the label before you read the chart. An AGM battery at 12.6 volts looks full on the flooded column but is only about 75 percent charged on the AGM column.
OPTIMA's 12.4-volt explainer says its REDTOP batteries are full at about 12.6 to 12.8 volts, while YELLOWTOP and light-gray BLUETOP models reach about 13.0 to 13.2. It warns that a 12-volt battery left below 12.4 volts begins to sulfate.
An enhanced flooded battery, or EFB, is a start-stop battery. Stryten Energy describes the EFB as a flooded lead battery with better cycling and charge recovery, and says nearly 30 percent of new U.S. start-stop vehicles come with one.
None of the charts used here gives EFB its own column. Because Stryten classes it as a flooded battery, use the flooded column as a guide. VARTA adds that AGM and EFB batteries need testers adapted to their technology, so set any load or conductance tester to the right type.
Hydrometer check for batteries with removable caps
A hydrometer reads each cell's specific gravity, which a multimeter can't. Dixie Electric's chart pairs 1.265 with full charge and 1.190 with 50 percent, while Discover Battery's testing guide targets the factory spec or 1.280, plus or minus .005. Discover adds .004 for every 10°F above 80°F and subtracts .004 for every 10°F below. Haynes notes that most new batteries are sealed, so only some older ones let you reach the cells.
Reading the Cranking Voltage Test
A healthy battery stays above about 10 volts while the starter turns the engine. A dip to 8 or 9 volts or lower suggests the battery may be bad.
| What the meter shows while cranking | What it suggests |
|---|---|
| Drops 1 to 1.5 volts, then recovers | Typical of a good battery |
| Above 10 volts | Normal cranking strength |
| Below 10 volts | Not enough turnover strength, prone to failure |
| 8 to 9 volts or lower | Battery may be bad |
| Below 5 volts | Replace the battery |
From AutoZone's, J.D. Power's and Tameson's multimeter guides.
Keep the crank short. The 2022 Ram 2500/3500 owner's manual says never to crank for more than 10 seconds at a time, to protect the starter, so a normal start with the meter watching is enough.
You will also see a 9.6-volt figure. That is the pass line for a load test, not a starter crank. Discover Battery's load test applies half the battery's cold cranking amp rating for 15 seconds and expects the voltage to stay above 9.6 volts. Dixie Electric's chart below gives the same figure for a battery at 70°F.
If the battery holds above 10 volts but the engine only clicks or turns slowly, check the cables and starter next. Our guide to telling a battery, starter or fuel problem apart walks through each one.
Does Cold Weather Change the Readings?
Yes, mostly under load. A full battery's resting reading barely moves, since AutoZone accepts 12.6 volts at 80°F and 12.516 volts at 0°F. The pass line for a load test drops much further as the temperature falls.
| Battery temperature | Minimum voltage under load |
|---|---|
| 70°F | 9.6 volts |
| 60°F | 9.5 volts |
| 50°F | 9.4 volts |
| 40°F | 9.3 volts |
| 30°F | 9.1 volts |
| 20°F | 8.9 volts |
| 10°F | 8.7 volts |
| 0°F | 8.5 volts |
From Dixie Electric's battery technical bulletin, for a 15-second load at half the battery's cold cranking amp (CCA) rating. A starter's load differs, so use it as a guide.
Dixie Electric's battery bulletin also says not to load test a battery below 75 percent charge, so charge it first. Then let it sit four to twelve hours in a warm room, because Dixie warns that leftover surface charge can make a weak battery look good or a good one look bad.
The bigger loss is strength. AAA Automotive Research Center figures show a battery losing about 35 percent of its strength at 32°F and about 60 percent at 0°F. AAA Hudson Valley adds that the engine may need up to twice the normal current to start in the cold.
Heat does its damage over time. AAA's battery warning signs guide says under-hood temperatures can exceed 200°F and that heat speeds up battery wear. Interstate adds that a discharged battery can freeze at 15°F.
Is the Alternator Charging? Reading Running Voltage
With the engine idling, most guides expect about 13.7 to 14.7 volts at the battery. Interstate says a reading below 13 volts can mean a bad alternator or battery.
| Source | Normal running voltage |
|---|---|
| Interstate Batteries | 13.7 to 14.7 volts |
| Fluke | 13.7 to 14.7 volts |
| Haynes | 13.8 to 14.4 volts at idle |
| AAA | 13 to 14.5 volts |
| J.D. Power | 14 to 14.5 volts |
| Honda smart charging | 12.5 to 14.5 volts, by design |
Ranges as each source publishes them. The Honda range is the system's designed setpoint range, reported by Vehicle Service Pros.
A reading from 14.0 to 14.4 volts falls inside every range in the table. Haynes says readings outside its range mean the system is under- or overcharging, which shortens battery life.
Smart charging systems can read lower
Smart charging systems vary alternator output, so a low running voltage isn't always a fault. Vehicle Service Pros explains that Honda's system can set anywhere from 12.5 to 14.5 volts and that GM, Ford and Toyota use some form of smart charging too.
To check one, add load. With the headlights and blower motor on, the article says the alternator should produce 13.5 volts or more.
How to Run a Parasitic Draw Test
A parasitic draw test measures the current your car pulls with everything off. Put the meter in series with the negative cable, let the modules sleep and look for under 50 milliamps.
- Prepare the car. Engine, accessories and interior lights off, doors closed. Haynes suggests noting your radio's anti-theft code before disconnecting the battery.
- Set the meter for amps. Black lead in COM, red lead in the 10A jack, dial on DC amps. Fluke's parasitic drain guide says to start on the highest range and work down.
- Connect the meter in series. Disconnect the negative cable and clip the meter between the negative post and the cable end, so all current flows through it.
- Wait for the modules to sleep. Fluke says this takes 10 to 45 minutes, depending on the vehicle.
- Read the draw. Fluke calls under 50 milliamps normal and over 100 milliamps suspect.
- Find the circuit. Pull fuses one at a time and watch for a big drop. Fluke says measuring voltage drop across each fuse also works, without pulling them.
- Inspect and reconnect. Check that circuit's wiring and parts. Fluke says aftermarket alarms, dash cams and stereos often cause drains.
Never crank the engine with the meter on amps
Fluke warns against cranking the engine or running high-current devices while the meter is in current mode. Reconnect the battery cable and remove the meter before anyone starts the car.
Check the Cables With a Voltage Drop Test
If the battery tests fine but the engine still cranks slowly, measure the voltage the cables lose while cranking. Fluke puts the acceptable total at 0.2 to 0.5 volts.
Fluke's starter voltage drop guide has you disable the fuel or ignition, for example by removing the fuel pump relay, then crank for 4 to 5 seconds per test.
- Positive side: red probe on the battery positive post, black probe on the starter's battery stud. The limit is about 0.3 volts.
- Ground side: red probe on the battery negative post, black probe on the starter housing or engine block. The limit is about 0.2 volts or less.
Fluke says anything higher suggests corrosion, loose terminals or damaged cables. Warm or hot cables after a few cranks can mean internal failure.
What a Multimeter Can't Tell You
A multimeter shows how charged a battery is, not how healthy it is. AutoZone notes that its store battery test has an advantage here, because it simulates a starting load on the battery. A multimeter can't measure cold cranking amps either. Its amp jacks are for small currents such as a parasitic draw, and Fluke warns against cranking the engine with the meter in current mode.
VARTA explains the gap. Cold start current is the decisive measure for a starter battery. On start-stop batteries, voltage shows state of charge, while state of health takes a complex test of cold cranking capability, residual capacity and charge acceptance.
AutoZone's battery services page says battery tests are available at every AutoZone in the U.S., and Interstate also offers complimentary tests. Dixie Electric says to replace any battery that doesn't go over 12.4 volts once charged.
If the car won't crank at all, the Car Symptom Diagnosis Tool lists the likely causes, from a weak battery to loose or corroded terminals.
Free tool
Car Symptom Diagnosis Tool. Pick "Car won't start" to see whether a weak battery, loose terminals or another part is the likely cause, and what to check first.
Mistakes That Give False Readings
Most bad readings come from testing too soon, reading the wrong chart or using the wrong setting.
- Testing right after a drive. Surface charge can make a tired battery look healthy.
- Using the flooded chart for an AGM. At 12.6 volts it shows full when an AGM is only about 75 percent charged.
- Probing through corrosion or paint. Fluke says both skew results.
- Touching both terminals with the dial on amps. SparkFun explains that this shorts the power source through the meter and blows its fuse.
- Blaming the alternator for a smart-charging reading. Near 12.5 volts can be normal on some cars.
- Judging a drained battery from one reading. Haynes says to fully charge it, let it rest overnight and test again.
- Starting and idling the car to top it up. OPTIMA says this can speed up discharge, because the alternator may not replace the energy used to start.
Cost of Testing a Battery Yourself or at a Shop
Testing at home costs only the price of a multimeter, and AutoZone tests batteries for free at its U.S. stores.
| Option | Typical cost | Notes |
|---|---|---|
| Basic multimeter | About $10 to $13 | Price points from Bridgestone and J.D. Power |
| Multimeters in general | $20 to several hundred dollars | AutoZone's range |
| Battery test at AutoZone | Free | Every U.S. store |
| New car battery | $45 to $250 | Depends on the battery your car needs |
| Alternator replacement | $500 to $2,500 | Includes parts and labor |
Meter prices from Bridgestone, J.D. Power and AutoZone. Testing from AutoZone's battery services page. Battery and alternator ranges from AAA's bad alternator vs. bad battery guide.
Bridgestone's battery guide says you can buy a multimeter online for about $10, and J.D. Power says you can find one for as little as $13. For the draw test, pick one with a 10A jack.
The diagnostic tools section of our accessories guide calls a multimeter the second diagnostic tool to buy, since it tests the battery, the alternator and fuses.
Make testing a habit. Interstate recommends a battery test at least twice a year or at every oil change, and AAA suggests a yearly test once a battery passes three years. A log of resting voltages makes a slow decline easy to spot.
Frequently Asked Questions
Is 10.5 volts a dead battery?
At rest, yes. Interstate Batteries considers a car battery dead at 11.9 volts or below, and Discover Battery puts a fully discharged battery below 11.80 volts. While the engine is cranking, though, 10.5 volts is an acceptable dip, since J.D. Power and Tameson only flag cranking readings that fall below 10 volts.
What voltage is 50 percent charge on a 12-volt car battery?
On a flooded battery, about 12.2 volts at rest means roughly half charged, according to Fluke, Haynes and Discover Battery. An AGM battery reads higher, and Discover puts its 50 percent mark above 12.30 volts. OPTIMA warns that lead-acid batteries start to sulfate below 12.4 volts, so a half-charged battery should go on a charger soon.
How can you tell a car battery needs replacing?
AAA lists eight warning signs: dim headlights at idle, clicking when you turn the key, electrical glitches, a slow crank, a lit battery or charging light, frequent jump-starts, a rotten sulfur smell and a bulging case. Any of them is a reason to test the battery soon. AAA says a swollen case often signals overheating or overcharging, so don't touch it.
Is a 4-year-old car battery still good?
It may be, but it is near the end of the usual range. AAA puts typical battery life at three to five years, with about three years more typical in the South and five years or longer in cooler northern climates. AAA recommends a test every year after the third, so a four-year-old battery is due for one.
Can a completely dead car battery be recharged?
Use a battery charger, not the car. OPTIMA says alternators are designed to maintain batteries, not recharge deeply discharged ones, and Interstate says the voltage needed to fully charge a deeply discharged battery is higher than an alternator produces. AutoZone says its fast charger can charge most car batteries in about 30 minutes. Retest after an overnight rest to see whether it holds.
Why does my battery read 12.6 volts but the car won't start?
A good resting reading only shows charge. The battery may lack cranking strength, or surface charge may be hiding a weak battery, so watch the voltage while someone turns the key. If it holds above 10 volts and the engine still won't turn, check for corroded terminals, loose cables or a failing starter, since a cable voltage drop above 0.5 volts points to a connection problem.
Sources and References
- Interstate Batteries. Support FAQs
- J.D. Power. How to Test a Car Battery with a Multimeter
- Schneider Electric. Digital vs. Analog Multimeter: Which Option is Right for You?
- Haynes Manuals. How to Test a Car Battery with a Multimeter (Step-by-Step Guide)
- Fluke. How to Measure Battery Voltage with a Multimeter
- SparkFun Electronics. How to Use a Multimeter
- AAA. Bad Alternator vs. Bad Battery: A Quick Guide
- AutoZone. How To Test a Car Battery's Voltage With a Multimeter
- Discover Battery. How Can You Tell If a Battery Is Fully Charged?
- VARTA Automotive. Testing the Battery: Step-by-Step
- OPTIMA Batteries. 12.4 Is the Magic Number for Batteries
- Stryten Energy. Enhanced Flooded Batteries (EFB) Are Designed for Start-Stop Vehicles
- Discover Battery. Battery Testing
- Mopar (Ram). 2022 Ram 2500/3500 Owner's Manual: If Engine Fails to Start
- Dixie Electric. Tech Tips: Batteries (TSB 030)
- AAA Hudson Valley. Cold Weather Is Hard on Your Car Battery: Here's What to Know
- AAA. Know When to Replace the Car Battery: 8 Key Warning Signs
- Vehicle Service Pros. What Makes Today's Charging Systems Smart?
- Fluke. How to Find Parasitic Battery Drain with a Multimeter
- Fluke. How to Check Starter Circuit Voltage Drop with a Multimeter
- AutoZone. Free Battery Testing & Installation Services
- Bridgestone. How to Test & When to Replace a Dead Car Battery
- Tameson. Learn How to Test a Battery Using a Multimeter
Written by
CarTipsMentor Team
Researched from the sources listed above and checked against them before publishing. Nobody paid to be mentioned on this page. It is general information, not advice about your own vehicle.
Published . Last updated .
