To test a battery, set your multimeter to DC volts, plug the black lead into COM and the red lead into V, and touch red to the battery's + end and black to −. With nothing else connected, you are reading its open-circuit voltage (OCV). That's enough to tell a fresh battery from a flat one, and, once the battery has rested, to estimate how full a car battery is. It can't tell you whether the battery can still deliver current. For that, measure again under load, while it's powering something. A battery that reads fine with nothing connected but drops sharply under load is worn out.
What you need
- A digital multimeter. Any cheap one will do for this. Every multimeter has a DC voltage setting.
- Something to use as a load (optional, covered below): the device the battery normally powers, a resistor, or a car's headlights.
- The multimeter's own battery in good shape. A meter with a flat battery can show wrong readings, and most show a small battery symbol when it's low.
How to measure a battery's voltage, step by step
- Plug in the leads. Black into the socket marked COM. Red into the socket marked V (often shared with Ω and other symbols). Not the socket marked A, 10A or mA: see the warning below.
- Turn the dial to DC volts. It's marked V with a straight line and three dashes beneath (⎓), or DCV. Not V~, which is for AC mains.
- Choose the range, if your meter asks. An auto-ranging meter picks for you. On a manual meter, pick the smallest range that's bigger than the battery's voltage: 2 V for a single 1.5 V cell (you get an extra decimal place), 20 V for 3 V coin cells, lithium-ion cells, 9 V and 12 V batteries.
- Touch the probes to the terminals. Red to +, black to −. Press firmly: dirt or corrosion on the terminal gives a low, jumpy reading.
- Read the display. If it shows a minus sign, the probes are the wrong way round. That's harmless, and the number is still right.
Finding + and − on common batteries
- AA, AAA, C, D: the end with the bump is +; the flat end is −.
- 9 V: the smaller round stud is +; the larger hexagonal one is −.
- Coin and button cells (CR2032, LR44 and so on): the wide flat face, usually with the writing on it, is +, and that metal wraps round the edge. The smaller raised face on the other side is −. Touch the black probe to the centre of the − face so its tip doesn't also brush the rim.
- Car batteries: + is usually red and marked +; − is black and marked −.
- Lithium-ion cells (18650, 21700): the end with the bump is +, as on an AA.
Never test a battery on the amps (A, 10A or mA) setting. In those sockets the meter is almost a plain wire, so touching the probes across a battery shorts it out. A fused meter will usually just blow its fuse; an unfused one can be destroyed. With a car battery or a lithium-ion cell, a short can also melt the probe tips and throw sparks. Voltage is always measured with the red lead in V.
What open-circuit voltage actually tells you
Open-circuit voltage is the voltage across a battery's terminals when nothing is drawing current from it. A multimeter on DC volts measures very nearly that, because it barely draws anything: even a basic meter like the Fluke 101 has an input resistance of more than 10 megohms, so it takes less than a millionth of an amp from a 9 V battery.
It helps to picture what's inside. Every battery behaves like a perfect voltage source with a small resistor hidden inside it, called its internal resistance. With no current flowing, nothing is lost across that resistor, and the meter sees the battery's full voltage. The moment something draws current, part of the voltage is used up inside the battery itself, and the terminals show less.
Two things follow:
- OCV gives a rough idea of how much charge is left. It works best on lead-acid batteries, whose voltage falls steadily as they empty, and worst on batteries with a flat voltage curve (more on that below). Even for alkaline AAs, Energizer's own handbook says OCV "can be misleading and at best will only yield a rough estimate".
- OCV says almost nothing about internal resistance. As a battery ages, gets cold or nears empty, that hidden resistor grows. An old battery can show a healthy-looking voltage with nothing connected and collapse as soon as you ask it for current. That's the car battery that reads 12.5 V and still won't start the car.
Let it rest first
A battery that has just been charged, or just been working hard, doesn't show its true resting voltage straight away.
- Just charged: the voltage reads high for a while, called surface charge, and settles over the following hours.
- Just used: it reads low and recovers as it rests. Lithium AAs are known for this: their voltage drops sharply under a load and then slowly climbs back.
So for a reading you can compare with a chart, let the battery rest with nothing connected: lithium-ion for about 90 minutes, lead-acid for at least four hours. Battery makers recommend a full 24 hours for lead-acid if you want an accurate state-of-charge reading. For a car battery after a drive, there's a quicker trick: switch the headlights on for a few minutes, then off, which removes most of the surface charge.
Temperature matters too. Cold batteries read lower and deliver much less, which is why a wireless sensor or a car can give up on a cold morning. Measure at room temperature if you can.
Battery voltage chart: what a healthy reading looks like
The table shows what a fresh, unused (or freshly charged) battery reads with nothing connected, and the voltage its maker rates it down to under load, which is roughly where it's considered empty. Devices often give up sooner: a camera or smoke alarm will complain about a battery that would still run a wall clock for months.
| Battery | Nominal | Fresh, nothing connected | Rated down to (under load) | Is OCV a useful fuel gauge? |
|---|---|---|---|---|
| Alkaline AA, AAA, C, D, and alkaline button cells (LR44 etc.) | 1.5 V | about 1.6 V | 0.8–0.9 V | Roughly. Load-test to be sure |
| Zinc chloride ("heavy duty") | 1.5 V | typically just over 1.6 V | about 0.9 V | Roughly |
| Lithium AA, AAA (Li-FeS₂) | 1.5 V | 1.79–1.83 V | 0.8 V | No. Stays high, then drops fast |
| NiMH rechargeable AA, AAA | 1.2 V | about 1.4 V straight off the charger | 0.9–1.0 V | No. Sits near 1.2 V most of its life |
| Alkaline 9 V (six cells inside) | 9 V | about 9.6 V | 4.8 V | Roughly. Divide by 6, use the AA row |
| NiMH 9 V (usually seven cells) | 8.4 V | — | about 7 V | No |
| Lithium coin (CR2032, CR2025…) | 3 V | about 3.3 V | 2.0 V | Not much. Flat, and a high internal resistance |
| Silver-oxide button (SR44, SR626…) | 1.55 V | 1.6 V | 1.2 V | No. Very flat |
| Zinc-air hearing aid (10, 312, 13, 675) | 1.4 V | about 1.4 V, 30 seconds after the tab comes off | — | No. Fairly flat |
| Lithium-ion cell (18650, 21700, phone and laptop cells) | 3.6–3.7 V | 4.2 V (a few types 4.3 V) | 2.5–3.0 V | As a rough guide. See below |
| LiFePO₄ cell | 3.2–3.3 V | charged to 3.65 V | 2.5 V (below 2 V damages it) | No. Very flat |
| 12 V lead-acid (car, AGM, sealed batteries in UPS units and alarms) | 12 V | 12.65 V, after resting | 11.89 V = fully discharged | Yes. The most useful of the lot |
A few things the table doesn't show:
- Alkaline voltage slides steadily as the battery empties (devices are designed to work across roughly 1.6 V down to 0.9 V per cell), so its OCV is at least a rough guide. Lithium AA, NiMH, silver-oxide, zinc-air and LiFePO₄ batteries hold an almost flat voltage until close to the end, so a "fine" reading tells you very little about what's left.
- A charged NiMH reading lower than a fresh alkaline is normal. NiMH drops from about 1.4 V off the charger to a plateau near 1.2 V once it's working, and stays there.
- Inside a 9 V battery there are six small 1.5 V cells in a row (lithium 9 V batteries use three 3 V cells; NiMH ones usually seven 1.2 V cells, hence 8.4 V).
Lithium-ion: a rough state-of-charge guide
A single lithium-ion cell that has rested for about 90 minutes gives a rough idea of how full it is. The middle of the curve is fairly flat, and exact figures vary with the cell type and temperature, so treat these as landmarks rather than a fuel gauge:
| Resting voltage | Roughly |
|---|---|
| 4.20 V | Full (for most cells) |
| about 3.82 V | About 40% |
| about 3.70 V | About 30% |
| 3.0 V | Bottom of the normal range. Recharge soon |
For storing lithium-ion for months, aim for about 40%, around 3.8 V per cell, not full. A lithium-ion cell barely self-discharges below about 4.0 V at room temperature, and it ages more slowly when it isn't kept full.
12 V lead-acid (car, caravan, UPS): state of charge
A rested 12 V lead-acid battery is the one case where open-circuit voltage really is a decent fuel gauge. These are the Battery Council International (BCI) figures for a starter battery at 26 °C after a 24-hour rest:
| Resting voltage | State of charge |
|---|---|
| 12.65 V | 100% |
| 12.45 V | 75% |
| 12.24 V | 50% |
| 12.06 V | 25% |
| 11.89 V | Fully discharged |
Notice how narrow the range is: full and flat are less than 0.8 V apart. Treat the table as approximate. "Maintenance-free" (calcium) and AGM batteries read a little higher than these figures, cold batteries read lower, and in a modern car the clock, alarm and computers keep drawing a little current even when it's parked, so the battery is never quite "open circuit" and reads slightly low.
While you're there, check the charging system: with the engine running, the alternator's regulator normally holds the battery at about 13.5–14.5 V.
LiFePO₄: why the meter can't tell you much
LiFePO₄ (lithium iron phosphate) batteries, the kind sold as 12 V drop-in replacements for caravans, boats and solar, have an extremely flat voltage curve. Most of the stored energy sits on that flat part, so the voltage really only tells you "full" and "nearly empty"; the middle can't be estimated. For these, use a battery monitor that counts the charge going in and out (often called a shunt or coulomb-counting monitor) rather than a voltmeter.
How accurate is your meter?
Even a good basic meter is only so accurate. The Fluke 101, for example, is specified at ±(0.5% + 3 digits) on DC volts. On a car battery reading 12.60 V, that's about ±0.09 V, roughly the difference between "full" and "about 90%" in the table above. On a single 1.5 V cell it's about ±0.01 V. Cheaper meters are often looser. Good enough to tell fresh from flat, but don't read too much into the last digit.
Do you need to put a load on it?
Often, no. A plain voltage reading is enough when you want to:
- sort a drawer of AA and AAA batteries into fresh and flat;
- check a charger actually charged something;
- see roughly how full a rested car battery is.
You do want a load test when:
- the battery reads fine but the device doesn't work. This is the classic sign of high internal resistance;
- it's a car battery and you want to know whether it will start the car, especially before winter;
- it's a coin cell in something that sends radio pulses, like a car key fob, a wireless sensor or a remote with an LED. Lithium coin cells have a high internal resistance even when new (around 10 ohms for a fresh CR2032, against about 0.3 ohms for an alkaline AAA), and it climbs as they're used. A tired one can read close to 3 V and still fail every time the device transmits;
- it's an old rechargeable (NiMH, lead-acid, lithium-ion) and you want to know if it's still worth keeping.
Three ways to load-test a battery
1. Measure it in the device, while it's working. The easiest load is the one the battery was made for. With the batteries in place and the device switched on (a torch is ideal), touch the probes to the battery terminals or to the contacts at each end of the battery compartment. Compare with the reading with the device off.
2. Use a resistor. Hold a resistor across the battery for one or two seconds and read the voltage across it. Energizer suggests about 10 ohms for a single AA-type alkaline cell. Check the resistor's power rating so it doesn't overheat:
| Battery | Resistor | Current | Heat in the resistor | Use at least |
|---|---|---|---|---|
| AA, AAA, C or D alkaline (1.5 V) | 10 Ω | about 0.15 A | about 0.25 W | a ½ W resistor |
| CR2032 coin (3 V) | 1 kΩ | about 3 mA | about 0.01 W | any resistor |
| 9 V | 100 Ω | about 0.09 A | about 0.8–0.9 W | a 1 W resistor (2 W runs cooler) |
The coin-cell and 9 V values are our suggestions, sized so each battery delivers a modest current like the devices that use it. Keep the load on only for a few seconds: you're testing the battery, not draining it.
3. Use a battery tester. Household battery testers (the ones with slots for AA, 9 V and button cells) put a load on the battery while they read it, with the load and the scale set for each battery type, which makes them more honest than a multimeter alone. Some multimeters have a BATT test range that does the same. For car batteries, auto shops use a load tester or an electronic tester that estimates the battery's cranking ability from its internal resistance.
Reading the result
A good battery's voltage dips a little under load. A worn one dips a lot. For an alkaline AA under a 10 ohm load, Energizer's guide is that a fresh battery reads about 1.5 V, and one reading 1.1 V has only about 20% of its life left.
You can also put a number on the hidden resistance:
Example. A fresh AA reads 1.60 V on its own and 1.56 V across a 10 Ω resistor. A worn one reads 1.40 V on its own and 1.27 V across the same resistor.
The current through the resistor is voltage ÷ resistance: 1.27 ÷ 10 = 0.127 A for the worn cell.
The voltage lost inside the battery is 1.40 − 1.27 = 0.13 V. Divide by the current: 0.13 ÷ 0.127 ≈ 1 Ω of internal resistance. The same sum for the fresh cell gives about 0.26 Ω, inside the 0.15–0.3 Ω Energizer quotes for a new AA. Four times the internal resistance means four times the voltage lost at the same current, which is why the worn cell can't run a torch but is still fine in a wall clock.
Load-testing a car battery with just a multimeter
The professional test draws half the battery's cold cranking amps (CCA) rating for 15 seconds from a battery that's at least 70% charged and at 10 °C or warmer. The battery passes if the voltage stays above 9.6 V. A 500 CCA battery, for example, is loaded at 250 A.
You can do a rough version with a multimeter and a helper:
- Make sure the battery is charged and has rested (or burn off the surface charge as above), and note its open-circuit voltage.
- Hold or clip the probes on the battery posts, well clear of the fan and belts.
- Have someone start the engine while you watch the lowest reading during cranking.
If the voltage falls well below about 9.6 V while cranking, the battery is either flat or worn out. Charge it fully and try again. If it still drops that low, it's time for a new one, or ask an auto shop for a proper load test.
Safety
- Lead-acid batteries give off hydrogen while charging, which is explosive. Don't make sparks near one, take off rings and watches, and never rest a spanner where it can touch both posts. Battery acid burns skin and eyes.
- Lithium-ion cells can deliver huge currents and catch fire if shorted, punctured or crushed. A swollen battery (a laptop that won't sit flat, a phone with a bulging back) should not be charged, probed or opened: switch it off and get it replaced.
- A lithium-ion pack reading 0 V may simply have been switched off by its protection circuit, which cuts out somewhere between 2.2 and 2.9 V per cell when the pack is run flat. Some chargers can wake it. But a cell that has sat below 1.5 V for a week or more may have developed internal shorts and shouldn't be recharged: recycle it.
- Power-tool, e-bike and laptop packs have their own electronics, and may read 0 V or the wrong voltage at the terminals until a charger or tool talks to them. Don't open them.
- Button and coin batteries are dangerous to small children. A swallowed one can lodge in the throat and cause serious internal burns within two hours, often with no obvious symptoms at first. If you think a child has swallowed or inserted one, call the Poisons Information Centre on 13 11 26 (24 hours, Australia-wide) or go straight to a hospital emergency department; call 000 if they are having trouble breathing or are bleeding. Keep the cells you're testing, and the dead ones afterwards, out of reach.
Recycling
Never put batteries in a household bin: crushed in a garbage truck or at a recycling plant, they start fires. Australia's national scheme is B-cycle, which takes household batteries, button cells, rechargeables, power banks, removable batteries from tools and cameras, and e-bike and e-scooter batteries. bcycle.com.au finds your nearest drop-off. Put clear tape over the terminals of every battery first, and cover button batteries on all sides. Car and other lead-acid batteries, laptop batteries and mobile phone batteries have their own schemes (ABRI, NTCRS and MobileMuster), and B-cycle's site links to each.
UPS beeping, laptop dying early?
The sealed lead-acid batteries inside office UPS units wear out with age like any other, and most UPS units regularly test their own battery and warn you when it's failing. Replacing UPS, laptop and alarm-panel batteries is everyday IT support work for us.
The cheat sheet
- Red lead in V, black in COM, dial on DC volts. Never the A or mA socket.
- Open-circuit voltage = the reading with nothing connected. A rough guide to how much charge is left.
- Let it rest before trusting the number: 90 minutes for lithium-ion, at least four hours for lead-acid.
- Under load = the reading while it's working. It tells you whether the battery can still deliver.
- Big drop under load = worn out, even if the open-circuit reading looked fine.
- Flat-voltage batteries (NiMH, lithium AA, silver-oxide, zinc-air, LiFePO₄) give little warning on a meter. Load-test them, or use a proper battery monitor.
Common questions
How do I test a battery with a multimeter?
What is open-circuit voltage?
Do I need to put a load on a battery to test it?
What voltage is a dead AA battery?
Why does my battery show the right voltage but not work?
What voltage should a car battery be?
What voltage is a fully charged lithium-ion battery?
Why do my rechargeable AAs only show 1.2 V?
Can I test a battery on the amps setting?
Sources
Battery makers' data (Energizer)
- Alkaline Manganese Dioxide Handbook and Application Manual: sloping discharge, devices work from about 1.6 V to 0.9 V per cell; OCV is only a rough estimate; test with about 10 Ω for 1–2 seconds, fresh about 1.5 V, 1.1 V ≈ 20% left; example OCV 1.6 V. link. Checked 20/10/2026.
- Energizer E91 (AA alkaline) datasheet: 1.5 V nominal, internal resistance 150–300 mΩ fresh, rated to 0.8 V. link. Checked 20/10/2026.
- Energizer A76 (LR44) datasheet: 1.5 V nominal, capacity to 0.9 V. link. Checked 20/10/2026.
- Carbon Zinc / Zinc Chloride Handbook: zinc chloride typically over 1.60 V; tests to 0.9 V. link. Checked 20/10/2026.
- Lithium Iron Disulfide (L91/L92) Handbook: fresh OCV 1.79–1.83 V, nominal 1.5 V; OCV drops under drain and slowly recovers. link. Checked 20/10/2026.
- Energizer L91 (AA lithium) datasheet: discharge to 0.8 V. link. Checked 20/10/2026.
- Nickel Metal Hydride Handbook: OCV about 1.4 V dropping to the 1.2 V plateau; 0.9 V per cell cut-off commonly used. link. Checked 20/10/2026.
- Energizer NH22 (9 V NiMH) datasheet: 8.4 V nominal, discharge to 1.0 V per cell. link. Checked 20/10/2026.
- Energizer 522 (9 V alkaline) datasheet: discharge to 4.8 V. link. Checked 20/10/2026.
- Lithium Coin Handbook: fresh CR2032 about 3.28 V; internal resistance near 10 Ω (AAA alkaline about 0.3 Ω), rising during discharge; pulse loads and cold cause voltage drop. link. Checked 20/10/2026.
- Energizer CR2032 datasheet: 3.0 V nominal, 235 mAh to 2.0 V. link. Checked 20/10/2026.
- Silver Oxide Handbook: open-circuit voltage 1.6 V, flat discharge. link. Checked 20/10/2026.
- Energizer 357/303 datasheet: 1.55 V nominal, capacity to 1.2 V. link. Checked 20/10/2026.
- Zinc Air Application Manual: nominal 1.4 V; activated by removing the tab; air for 30 seconds; relatively flat discharge. link. Checked 20/10/2026.
Battery University
- BU-903: How to Measure State-of-charge: rest at least 4 h, 24 h for lead-acid; BCI table (12.65 / 12.45 / 12.24 / 12.06 / 11.89 V at 26 °C); calcium and AGM read higher; parasitic loads in modern cars; flat Li curves; coulomb counting. link. Checked 20/10/2026.
- BU-804c: Acid Stratification and Surface Charge: headlights for a few minutes or rest a few hours. link. Checked 20/10/2026.
- BU-902a: How to Measure CCA: half CCA for 15 s, 70–100% charged, 10 °C or warmer, pass above 9.6 V. link. Checked 20/10/2026.
- BU-902: How to Measure Internal Resistance: DC load method (OCV, then loaded voltage, Ohm's law). link. Checked 20/10/2026.
- BU-205: Types of Lithium-ion: 3.6/3.7 V nominal, 3.0–4.2 V range, charge to 4.20 V (some 4.30 V), 2.5–3.0 V cut-off; LiFePO₄ 3.2/3.3 V nominal, charge to 3.65 V, below 2 V causes damage. link. Checked 20/10/2026.
- BU-702: How to Store Batteries: store Li-ion at about 40%; 3.82 V at 40%, about 3.70 V at 30%; rest 90 minutes before reading. link. Checked 20/10/2026.
- BU-808a: How to Awaken a Sleeping Li-ion: protection cuts off at 2.2–2.9 V/cell; don't boost cells that dwelled below 1.5 V for a week or longer. link. Checked 20/10/2026.
- BU-403: Charging Lead Acid: hydrogen generated during charging is explosive. link. Checked 20/10/2026.
Meters, cars, recycling
- Fluke 101 Digital Multimeter Users Manual: DC volts ±(0.5% + 3), input impedance >10 MΩ. link. Checked 20/10/2026.
- Multimeter, Wikipedia: measuring current/resistance across a low-impedance source; fused vs unfused meters. link. Checked 20/10/2026.
- Automotive battery, Wikipedia: regulator holds 13.5–14.5 V while running. link. Checked 20/10/2026.
- Nine-volt battery, Wikipedia: alkaline PP3 = six 1.5 V cells; lithium = three cells. link. Checked 20/10/2026.
- B-cycle (Australia's battery stewardship scheme): what's accepted, tape the terminals, ABRI / NTCRS / MobileMuster for other batteries. link. Checked 20/10/2026.