Cordless tool battery supplying energy to garden equipment and a work light

What Watt-Hours (Wh) Mean on a Cordless Battery

ByKen

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If you are asking what does wh mean on a battery, the short answer is that Wh stands for watt-hours, the energy a battery can store. You get it by multiplying the pack’s voltage by its amp-hour rating. Some battery pages print the Wh figure, and others print only volts and amp-hours, so you may need to do the multiplication yourself. This guide explains the figure, shows how to read it on a label, and marks the point where it stops being useful for comparing tools.

Quick answer

  • Wh (watt-hours) is the energy a battery can store. EGO’s pack page gives the formula: Voltage x Capacity (Ah) = Energy (Wh).
  • EGO states that its 56V, 7.5Ah pack holds 420 Wh, and 56 x 7.5 gives the same figure.
  • A Wh figure depends on the voltage the maker used. Check that voltage before you compare two packs.
  • Wh does not give run time on its own. The sources we opened do not state a power draw for any mower, trimmer or blower.

What Wh measures

Watt-hours combine power and time. A watt is a unit of power, and a watt-hour is the energy used when one watt runs for one hour. For a battery, the figure tells you the total energy the pack can hold and deliver, not how fast it delivers that energy. EGO’s pack page draws the same line: “Power is measured in Watts and that is calculated by Voltage x Current. In addition, to calculate how long that power can be delivered, use Voltage x Capacity (Ah) = Energy (Wh).”

Cell wiring explains why volts and amp-hours can change separately. EGO’s page says: “Arranging enough cells together in series delivers the required voltage (V). Adding an identical number of cells in parallel delivers more capacity and higher power (W).” In plain terms, series wiring sets the voltage, and parallel wiring adds capacity. Two packs can share a voltage and still hold different amounts of energy, or share an amp-hour rating and carry different voltages. That is why the Wh figure, read with its voltage, tells you more about stored energy than either number alone.

Safety notes for charging and storing

A Wh figure does not change how you should charge or store a pack. Follow the maker’s instructions. The sources we opened agree on the following points.

  • Charge in the stated temperature range. EGO’s 7.5Ah page gives an “Optimum charging temperature: 32°F-104°F(0°C-40°C).”
  • Store and charge in a cool, dry place. DeWalt says: “Store and charge batteries in a cool, dry location.” EPA says: “It is best to store Li-ion batteries at room temperature.” OSHA’s workplace guidance lists “Storing batteries in cool, dry locations.”
  • Do not use a pack that looks damaged. DeWalt says: “Do not use batteries with visible damage or cracks.” EPA says: “The swelling indicates damage to the battery and is a potential fire hazard.”
  • Return a wet or damaged pack. EGO says: “Batteries that have been exposed to water for longer than recommended should be returned to EGO dealers for inspection.”

Do not open a pack or attempt a repair. If a pack is swollen, cracked or wet, stop using it and contact the maker, as EGO’s page directs for wet or damaged packs.

How to read Wh on a label

  1. Find the voltage first. EGO’s 7.5Ah page prints “Voltage: 56V, 420 Wh” on one line, so the voltage and the energy figure appear together. Wh has no meaning until you know the voltage behind it.
  2. Find the Ah rating. The same page prints “Amp Hours: 7.5 Ah”. Ah is the capacity rating the maker gives the pack.
  3. Multiply and compare. Multiply the voltage by the Ah rating. For EGO’s pack, 56 x 7.5 = 420, which matches the printed Wh.
  4. If only Ah is printed, do the multiplication yourself and label it. Write down the voltage you used and mark the result as your calculation, not the maker’s figure.
  5. Compare packs on the same basis. Do not set a 20V Wh figure beside a 56V Wh figure until you know which voltage each maker used.

Wh figures from two makers

The EGO battery chart lists Wh beside each Ah rating for its packs. The chart does not print a voltage, so the table shows what each source says about voltage. The DeWalt figure comes from a separate page.

Pack rating Energy (Wh) as stated Voltage stated Source
EGO 2.5 Ah 140 Wh not stated EGO battery chart
EGO 5.0 Ah 280 Wh not stated EGO battery chart
EGO 6.0 Ah 336 Wh not stated EGO battery chart
EGO 7.5 Ah 420 Wh 56V EGO 7.5Ah battery page and EGO battery chart
EGO 12.0 Ah 672 Wh not stated EGO battery chart
DeWalt 9.0 Ah FLEXVOLT 180 Wh not tied to the Wh figure; footnote gives 20V maximum and 18V nominal DeWalt 9.0Ah battery page

Each EGO value in the chart equals 56 times its Ah rating. This is a calculation, and it fits the 56V figure printed on the 7.5Ah page. The chart itself does not print 56V, which is why the table marks the voltage as not stated for those rows.

Worked calculations

The formula is Energy (Wh) = Voltage (V) x Capacity (Ah). Two examples use figures printed by the makers.

EGO, 7.5Ah pack. Inputs: 56 V and 7.5 Ah. Calculation: 56 x 7.5 = 420 Wh. The result matches the 420 Wh printed on EGO’s page.

DeWalt, 9.0Ah pack. Inputs: 20 V and 9.0 Ah. Calculation: 20 x 9.0 = 180 Wh. The result matches the 180 Wh printed on DeWalt’s page. The footnote on that page gives 20 V as the maximum initial voltage and 18 V as the nominal voltage. Using 18 V gives 18 x 9.0 = 162 Wh, which does not match the printed figure. The page does not say which voltage its figure uses, so the 20 V basis is the one that reproduces the printed number.

Why the voltage basis changes the answer

A maker can base a Wh figure on a nominal voltage or on a maximum voltage, and the two give different totals. DeWalt’s footnote shows both: “Maximum initial battery voltage (measured without a workload) is 20, 60, and 120 volts.” and “Nominal voltage is 18, 54, and 108.” The EGO pages print “Voltage: 56V” without saying which basis applies. When you compare two packs, compare Wh only after you know each maker’s voltage basis. If the basis is not printed, treat the Wh figure as the maker’s claim and say so in your notes. For how mower pack voltages are labelled, see what voltage a lawn mower battery is.

What Wh does not tell you

Wh tells you the energy stored in the pack. It does not tell you how long a given tool will run, because run time also depends on how much power the tool draws. EGO’s page links Wh to “how long that power can be delivered,” but it gives only the formula. It does not give a power draw for any mower, trimmer or blower.

Two packs with the same Wh can give different run times in different tools. In the same tool, more stored energy usually means more run time. EGO’s battery chart makes this point when it says that for even longer run times, you can choose a battery with a higher number of amp hours than the one recommended. EGO’s chart says that it “tells you which battery is best for your tool,” so the chart is a pack-size guide, not a run time table. For a mower, start with the run time the maker states for that mower and pack, then read the runtime guide before you estimate anything. For voltage first, see lawn mower battery voltage and amps, and for a wider view of voltage, see lawn and garden battery voltage.

How we chose

We opened more pages than we cite and chose six for three jobs. Two EGO pages and one DeWalt page supply the Wh and voltage figures that appear on the pack pages a buyer reads. Two government pages, EPA and OSHA, supply the storage and damage points. We did not use retail listings, review sites or blogs. The pages were opened on 2026-10-22, and they are listed at the end of this guide. The sources were read as written and are not ranked against each other.

What we could not verify

The pages we opened do not print a Wh figure for every EGO pack or every DeWalt pack. We could not confirm whether EGO’s 56V figure is a nominal or a maximum voltage, because the page does not say. The DeWalt 180 Wh figure has no printed voltage, so the 20V basis above is a calculation that reproduces the number, not a stated fact. A Ryobi battery page returned a server error when opened, so no Ryobi figure appears in this guide.

Mistakes to avoid

  • Reading Wh as a run time. EGO’s 420 Wh is the stored energy on its 7.5Ah pack. The run time a maker states for a mower is a separate claim for one mower and one pack.
  • Setting 180 Wh beside 420 Wh without the voltage. The two figures use different voltage bases. DeWalt’s 180 Wh matches 20V times 9.0Ah, and EGO’s 420 Wh matches 56V times 7.5Ah.
  • Assuming a Wh figure uses the nominal voltage. DeWalt’s footnote separates maximum and nominal voltage. EGO’s pages do not say which one applies to its 56V figure.

What the sources do not say

  • The sources we opened do not state how Wh affects charging time for a given charger.
  • The DeWalt 12.0Ah page we opened does not print a Wh figure, and the Husqvarna pages we opened do not print a Wh figure for their packs.
  • The sources do not state a power draw for any mower, trimmer or blower, so no run time is calculated in this guide.

FAQ

What does Wh mean on a battery?

Wh means watt-hours. It is the energy a battery can store, and it is found by multiplying voltage by amp-hours. EGO’s 7.5Ah pack is stated at 420 Wh, and 56V times 7.5Ah gives the same number.

Use Wh to compare stored energy between packs, but only after you know the voltage each maker used.

How do I calculate Wh from volts and amp-hours?

Multiply the voltage by the amp-hour rating. For a 56V, 5.0Ah pack, 56 x 5.0 = 280 Wh, which matches the 280 Wh in EGO’s battery chart for the 5.0Ah pack.

If the label gives only Ah, use the voltage printed on the same label. Mark the result as your own calculation.

Is a higher Wh always a longer run time?

No. Wh is the energy stored, and run time depends on how much power the tool draws. The sources we opened do not state a power draw for any tool in this guide, so they cannot show a run time from Wh alone.

In the same tool, a pack with more stored energy usually gives more run time, and EGO’s chart notes that a higher Ah rating can give longer run times. Still, check the run time the maker states for that exact tool and pack.

Why do EGO and DeWalt Wh figures differ so much?

The two makers use different Ah ratings and different voltage figures. EGO’s 7.5Ah pack is stated at 420 Wh on a 56V basis. DeWalt’s 9.0Ah pack is stated at 180 Wh, and the 20V maximum voltage reproduces that figure. The gap comes from the voltage platform and the capacity together, not from the Ah number alone.

Can I compare Wh across brands?

Only when each maker states the Wh figure and the voltage basis behind it. The DeWalt page states 180 Wh without tying that figure to a voltage, so it is hard to line it up against an EGO figure on a 56V basis. Check each maker’s own page for the figure and its basis before you decide.

Does Wh tell me how to charge or store a battery?

No. Wh tells you how much energy the pack holds. For charging and storage, follow the maker’s instructions. EGO gives an optimum charging range of 32°F to 104°F (0°C to 40°C), and DeWalt advises a cool, dry location.

Bottom line

Before you compare two cordless batteries, confirm that each Wh figure has a printed voltage behind it. If the voltage basis is missing, treat the Wh as the maker’s claim and do not set it directly against a figure from another maker.

Sources

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