Car Battery Voltage Chart

How to use this car battery voltage chart

1. Say when you took the reading. Resting, cranking, charging, or a proper load test. This is the step every other chart skips, and it's the one that decides whether 12.4 volts is fine or a problem.
2. Enter the voltage. Probes on the battery posts, not the clamps. A corroded clamp reads as a bad battery and gets a lot of good batteries thrown away.
3. Pick the battery type. Flooded, AGM or gel, or lithium. An AGM rests about two-tenths of a volt higher than a flooded battery at the same charge, so reading one against the other's chart costs you fifteen points of state of charge.
4. Set the battery's temperature. Not the forecast, the battery. After a cold night use the overnight low. The chart is published at 80 °F and the correction is worth a lot in winter.
5. Read the result and the highlighted row. The chart below marks where your corrected reading lands. "Copy result" grabs it as text, "Share" copies a link with your reading baked in, and "PDF" downloads all three tables for the toolbox.

Why this chart is different from other battery voltage pages

Every page on this search ships the same thing: a static table you read yourself. Some are pictures of tables. One of the top results is a five-year-old forum screenshot, and the first comment under it asks for a printable version. Here's what's actually missing from all of them:

• Nobody asks when you took the reading. 12.4 volts at rest is a battery at 75%. The same 12.4 volts with the engine running is an alternator that isn't charging. 9.8 volts is a pass while cranking and a dead battery at rest. One number, four verdicts, and the static charts pick one and leave you to guess.
• Nobody corrects for temperature, even though the reference charts are all published at 80 °F and the reason you're looking this up is usually that the car didn't start on a cold morning. A reading of 12.30 volts is 57% at room temperature and 74% at 20 °F. That's the difference between "replace it" and "charge it."
• Nobody publishes the temperature-adjusted load-test minimums. Everyone quotes 9.6 volts. Almost nobody mentions that 9.6 is the figure at 70 °F and that the bar drops to 8.5 volts at 0 °F, which is exactly when you'd be testing.
• Nobody warns you about smart charging. Most cars built since about 2010 vary alternator output on purpose and will happily sit at 12.8 volts once the battery is full. Read that against a chart that says "under 13.0 = alternator failure" and you buy an alternator you didn't need.
• Nobody switches chemistry. The lithium chart in particular is worth showing precisely to make the point that voltage barely works as a fuel gauge on LiFePO4 — a tenth of a volt covers 40% to 70%.
• Free to embed. No competitor on this search offers one. Forums, club sites, RV and marine boards, and shop blogs can drop this in with a line of HTML.

How it works — the math behind the numbers

Resting voltage to state of charge

A lead-acid battery's open-circuit voltage tracks its state of charge closely enough to use as a fuel gauge, provided it's been resting. The industry reference points for a flooded 12-volt battery, measured at 80 °F, are 12.66 V at 100%, 12.45 V at 75%, 12.24 V at 50%, 12.06 V at 25%, and 11.89 V at 0%. Notice the steps aren't even — 0.21, 0.21, 0.18, then 0.17 volts — so this tool interpolates piecewise between the published points rather than drawing one straight line through them. Rows marked with a dot in the chart are the published values; the rest are interpolated between them.

AGM and gel batteries rest higher, near 12.85 V when full, and lithium iron phosphate is a different animal entirely: its curve is so flat that 13.1 V is 40% and 13.2 V is 70%. On a lithium battery, believe the BMS readout over any chart, including this one.

The temperature correction

Cold slows the chemistry down and the resting voltage falls with it, so a chart printed at 80 °F overstates how flat a cold battery is. The published rule is to subtract 0.024 volts from the chart for every 10 °F below 80, which is the same as adding it back to your reading before you look it up:

corrected volts = measured volts + 0.0024 × (80 − battery temp in °F)

At 20 °F that's 0.144 volts, which moves a 12.30 V reading from 57% to 74%. Lithium gets no correction here — the coefficient is trivial next to how flat the curve already is, and applying the lead-acid figure would just be wrong.

The load test

Voltage tells you how full a battery is. It does not tell you how much it can still deliver, and that's the thing that strands people. The standard test is to apply half the battery's rated cold cranking amps for 15 seconds and read the voltage at the fifteen-second mark, with the load still connected. Let go first and the voltage bounces back, which makes a bad battery look fine.

The pass mark is 9.6 volts at 70 °F, and it slides down with temperature: 9.3 volts at 40 °F, 9.1 at 30, 8.5 at 0 °F. Two caveats matter. The test is only meaningful on a battery that's at least 75% charged, so charge it first or you're measuring a flat battery rather than a bad one. And a manual load test needs the surface charge gone first — a flooded battery reading over about 12.8 V, or an AGM over 13.0, still has one sitting on top.

Charging voltage

With the engine running you're no longer measuring the battery, you're measuring the charging system. 13.6 V to 14.7 V at the posts is normal. Under 13.0 V means nothing is going back in, though before condemning the alternator check the belt, the main output lead and the engine ground straps, because a bad ground fakes a dead alternator convincingly. Over 15.0 V is a failed regulator, which boils the electrolyte and can kill a new battery in weeks.

Worked examples

The car that won't start on a January morning. The battery reads 12.30 V and it's 20 °F outside. Read straight off a standard chart that's 57% and looks like a battery on its way out. Corrected to the chart's 80 °F reference it's 12.44 V, or 74% — low, worth charging, but not a replacement. Charge it properly and load test before spending money. This is the single most common way a healthy battery gets condemned in winter.

An AGM that looks fine and isn't. A sealed AGM reads 12.45 V at rest. On a flooded chart that's a comfortable 75%. On the AGM chart it's 59%, because an AGM at full charge rests near 12.85 V, not 12.66. The battery is meaningfully flatter than the number suggests, and if it's a stop-start car the charging system will be working against a battery that's already behind.

A load test that passes in one shop and fails in another. A truck battery holds 9.2 V under a half-CCA load. At 40 °F the minimum is 9.3 V, so it fails. Roll the same battery outside to 30 °F and the minimum drops to 9.1 V and the same 9.2 V now passes. Nothing changed about the battery — which is why the temperature has to be part of the verdict rather than a footnote.

A charged battery reading 10.5 volts. It's been on a charger overnight and it still reads 10.5 V. That's the signature of a shorted cell: one dead cell of six costs about 2.1 volts, and no amount of charging brings it back. Replace it, and while you're there check whether your tester can read conductance, because that's the test that catches this before it strands you.

Frequently asked questions

Is 12.2 volts okay for a car battery?

Not really. On a rested flooded battery at room temperature, 12.2 V is roughly 50% charged. The car will probably still start in mild weather, but a lead-acid battery left below 75% sulfates and loses capacity permanently, so sitting at 12.2 is doing damage every day it stays there. Put it on a proper charger and then work out why it got there: a parasitic drain, a lot of short trips, or a charging system that isn't keeping up.

At what voltage should I replace my car battery?

There isn't a resting voltage that means "replace", and that's the honest answer most pages dodge. Voltage shows state of charge, not remaining capacity, so a worn-out battery can read a perfect 12.66 V and still collapse the moment the starter turns. The readings that genuinely condemn a battery are the ones under load: dropping below the temperature-adjusted minimum during a load test or while cranking, or a rested reading near 10.5 V that won't come up on a charger, which is a shorted cell. Anything else means charge it first, then test.

What voltage indicates a dead battery?

A rested 12-volt battery at or below 11.9 V is flat — zero percent by the standard chart, even though it still shows nearly twelve volts. That surprises people: these batteries are full at 12.6 and dead at about 11.9, not dead at zero. Below about 10.8 V on a battery that has been charged, suspect a shorted cell rather than a discharge. A deeply flat battery can often be recovered by charging it slowly, but it rarely comes back to full capacity, so load test it before you trust it.

What should a car battery read with the engine running?

13.6 to 14.7 volts measured at the posts. Below 13.0 the alternator isn't putting anything back, though check the belt and grounds before buying one. Above 15.0 the voltage regulator has failed and the battery is being cooked. One important caveat: most vehicles built since roughly 2010 manage the alternator with a battery sensor and deliberately drop as low as 12.5 volts once the battery is full, to save fuel. On those, a single low reading is normal behaviour, not a fault — rev to 1,500–2,000 rpm with the lights and blower off and see whether it climbs.

Is a 20 minute drive enough to charge a car battery?

Rarely. Starting the engine takes a big bite out of the battery and the alternator is also running the ignition, lights, heater and everything else, so what's left over for recharging is modest. Twenty minutes of driving might replace what the start cost you and not much more, which is why a car doing nothing but short trips slowly walks its battery down to 12.2 V. Bringing a discharged battery back up properly takes several hours on a charger. If your driving is mostly short hops, a maintainer left on overnight now and then is the fix, and a lithium jump pack in the glovebox is the insurance.

Related tools

• Jump Start Order — the animated cable sequence, in the order that doesn't spark over the battery.
• Used Car Inspection Checklist — printable, and the battery and charging checks are on it.
• Bolt & Lug-Nut Torque Calculator — battery hold-downs and terminal clamps have specs too, and they're low ones.
• Spark Plug Gap Chart — when it cranks fine but still won't fire.
• Browse all free tools by Mike Reeves →

Mike's recommendations for battery work

A multimeter gets you the state of charge. Everything past that needs one of these three:

• Best Car Battery Testers — a conductance tester reads capacity, which is the half of the answer voltage can't reach. This is the tool that tells you whether to charge it or replace it.
• Best Car Battery Chargers — a smart charger brings a discharged battery back properly and holds it there. Short drives don't.
• Best Jump Starters — once a battery has been down below 50% you're on borrowed time in cold weather. A lithium pack in the glovebox is cheap insurance.

If the battery keeps going flat with nothing obviously wrong, the next step is finding the drain, and a scanner plus our battery maintenance guide will get you there faster than replacing parts.

Sources & methodology

• AA1Car — How to Test Your Car Battery — the five-point state-of-charge table at 80 °F, the −0.024 V per 10 °F temperature rule, the 75% service floor, and the half-CCA load test at 9.6 V.
• Purkeys — Load Testing Vehicle Batteries in Three Steps — the temperature-adjusted load-test minimums, the surface-charge thresholds (12.75 V flooded, about 13 V AGM), and the read-at-15-seconds procedure.
• Free ASE Study Guides — Battery Capacity Test — the CCA definition (30 seconds at 0 °F above 7.2 V) and the half-CCA, 15-second, 9.6 V-at-70 °F test.
• AutoZone — What You Need to Know About Car Battery Voltage — the 12.6 V resting reference.
• Renogy — The Comprehensive Guide to Battery Voltage Charts — the AGM and LiFePO4 open-circuit tables.

Where the numbers are a consensus rather than a single source, we say so. The flooded five-point table and the load-test minimums are industry standards that every source above agrees on. AGM and gel figures vary by roughly a tenth of a volt between manufacturers, so the AGM anchors here are a stated middle rather than any one brand's table — if your battery's own label prints numbers, those win.

Every formula, anchor and threshold above is asserted by fixtures.test.mjs next to the tool's data file, and the test runs before the site can build. It reproduces Purkeys' published worked example in both directions, checks that every published anchor returns its own state of charge, and proves the state-of-charge curve never runs backwards. About Mike Reeves · Last reviewed September 4, 2026.

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