Use this battery energy converter to convert mAh, Ah, Wh, kWh, watts, kilowatts, and runtime with voltage, usable capacity.
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Battery energy converter Convert between mAh, Ah, Wh, kWh, watts, and runtime with voltage, usable capacity, and efficiency kept visible. This consolidated battery capacity converter covers mAh to Wh, Ah to Wh, Wh to mAh, kWh to watts, watts to kWh, kWh to kW, and kW to kWh questions without splitting the same energy problem across near-duplicate pages.
Quick conversion intents
20K power bank
Common voltage bases
Use the voltage attached to the capacity label. A power-bank mAh rating is usually an internal-cell basis, while USB output checks should keep efficiency losses visible.
Voltage and time are required context
mAh and Ah are charge units, while Wh and kWh are energy units. Watts and kW are power rates, so kWh to watts or kW to kWh conversions also need a runtime assumption.
Result
74 Wh
20,000 mah at 3.7 V is 0.07 kWh before usable-capacity and efficiency adjustments.
Amp-hours
20 Ah
Milliamp-hours
20,000 mAh
Usable energy
74 Wh
Runtime estimate
Needs load or charge power
Average power
Needs runtime
Average kilowatts
Needs runtime
Planning question
Result
Use this for
Wh to kWh
0.07 kWh
Battery storage and utility-style energy comparisons
Usable kWh
0.07 kWh
Runtime and reserve estimates after loss assumptions
Required capacity
Enter load and runtime
Sizing a battery from a watts-to-kWh runtime target
Energy from load
Enter load and runtime
Watts-to-kWh sizing after usable-capacity and efficiency assumptions
Average watts
Enter runtime
kWh-to-watts and kWh-to-kW conversion from stored energy and time
Charge time
Needs load or charge power
Rough kWh-to-kW or kW-to-kWh planning
Discharge rate
Enter load
Battery stress checks from load, voltage, and capacity
Charge C-rate
Enter charge power
Charge-rate context from kW, voltage, and battery capacity
Formula
Wh = (mAh / 1000) x V
Working equation
Wh = (20000 / 1000) x 3.7 = 74 Wh
Loss assumptions
100 % usable capacity and 100 % efficiency.
Travel check
Below 100 Wh
Usually below the common spare lithium-ion battery threshold used for passenger-aircraft carry-on checks, but the printed battery label and carrier rules still control.
Battery energy converter: mAh, Ah, Wh, kWh, watts, and runtime
Use this battery energy converter to move between mAh, Ah, Wh, kWh, watts, kilowatts, and runtime with the missing assumptions kept explicit. It consolidates common battery capacity converter searches such as mAh to Wh calculator, Ah to Wh calculator, Wh to mAh calculator, watts to kWh calculator, kWh to watts calculator, kWh to kW calculator, and kW to kWh calculator into one broader energy-planning page.
What this battery energy converter covers
This page converts charge capacity and energy capacity across milliamp-hours, amp-hours, watt-hours, and kilowatt-hours. It also connects stored energy with watts, kilowatts, and runtime when a load or charge-power assumption is supplied.
That broader scope is why this page now owns the overlapping battery-conversion cluster. A user searching for ah to wh, mah to wh, wh to mah, kwh to watts, watts to kwh, kwh to kw, or kw to kwh is usually trying to answer the same battery-energy question with a different known value.
The calculator keeps voltage visible because mAh and Ah cannot become Wh or kWh without a voltage basis. It keeps time visible because watts and kilowatts cannot become kWh without a runtime basis.
The core formulas
Battery charge units and energy units are connected by voltage. Once the result is in watt-hours, the conversion to kilowatt-hours is just a scale change: divide by 1,000.
Power and energy need time. A kWh to watts calculation needs the number of hours over which the energy is used, while a kW to kWh calculation needs how long that power level is sustained.
The result panel displays the working equation for the selected starting unit so you can check whether the right voltage and time basis were used.
Wh = Ah x V
Use when battery charge capacity is known in amp-hours.
Wh = (mAh / 1,000) x V
Use for compact battery and power-bank labels stated in milliamp-hours.
kWh = Wh / 1,000
Use after converting battery capacity to watt-hours.
kWh = kW x h
Use when average power and runtime are known.
Why voltage is required for mAh, Ah, Wh, and kWh
mAh and Ah measure charge capacity, not stored energy by themselves. A 20,000 mAh battery at 3.7 V is about 74 Wh, while the same 20,000 mAh at 12 V is 240 Wh. The mAh figure is identical, but the stored energy is not.
That is why this converter asks for nominal voltage even when the starting value is already in Wh or kWh. The energy result can be calculated without voltage, but reverse conversions back to Ah and mAh still need a voltage basis.
For planning, use the nominal battery or pack voltage published by the manufacturer. Do not mix an internal cell voltage, a USB output voltage, and a system bus voltage unless that is the specific conversion you intend to model.
Choosing the right voltage from a battery or power-bank label
Competitor pages often stop at the mAh to Wh formula, but the harder practical question is which voltage belongs in the formula. For a power bank, the advertised mAh value usually describes the internal lithium-cell pack, commonly around 3.7 V, while USB output may be 5 V, 9 V, 12 V, or 20 V after conversion electronics.
Use the voltage basis that matches the capacity label you are converting. If the label says 20,000 mAh and separately lists a 74 Wh rating, that mAh figure is almost certainly on the internal cell basis. If you want to estimate delivered USB output, apply the converter efficiency field after calculating stored Wh rather than replacing the cell voltage with the USB output voltage.
For larger systems, use the nominal pack voltage for the battery bank or vehicle pack. A 100 Ah 12 V battery, a 100 Ah 24 V battery, and a 100 Ah 48 V battery have very different stored energy even though the amp-hour value is identical.
Power-bank label mAh: usually convert with the internal cell or pack voltage printed by the maker.
USB output planning: keep stored Wh separate from delivered Wh, then apply efficiency losses.
Home battery or solar bank: use nominal system voltage, such as 12 V, 24 V, or 48 V.
EV pack conversions: use nominal pack voltage only for rough Ah comparisons; range and charging decisions need vehicle-specific data.
How watts and runtime fit battery sizing
Watts describe the rate at which a load uses energy. Watt-hours and kilowatt-hours describe how much energy is used over time. The calculator uses the load in watts to estimate runtime from usable Wh, or it uses load plus target runtime to estimate the battery capacity required.
For example, a 1 kWh battery with 90% usable capacity and 85% conversion efficiency has about 765 Wh available to the load. A 100 W device would run for about 7.65 hours under those assumptions.
This is still a planning estimate. Real runtime can shift with inverter losses, discharge curves, temperature, battery age, cutoff voltage, and load variation.
Using kWh to watts, watts to kWh, kWh to kW, and kW to kWh correctly
kWh to watts and kWh to kW questions need a time period. Two kWh spread over 8 hours is a 250 W average load. The same two kWh spread over 2 hours is a 1 kW average load.
Watts to kWh and kW to kWh questions move the other way. Multiply the load by runtime to estimate total energy demand, then compare that result with the battery Wh or kWh shown by the converter.
These time-based conversions are included here because battery sizing, EV charging, solar storage, and appliance backup planning often move back and forth between stored energy and power draw.
kWh to W: watts = kWh x 1,000 / hours
W to kWh: kWh = watts x hours / 1,000
kWh to kW: kW = kWh / hours
kW to kWh: kWh = kW x hours
Power-bank and travel checks
Power-bank searches often start with mAh but need Wh. That is because travel and transport guidance commonly uses watt-hours, which represent energy directly across different battery voltages.
A 20,000 mAh power bank at a typical 3.7 V lithium-ion cell basis is about 74 Wh. A 27,000 mAh pack at 3.7 V is about 99.9 Wh, which is close enough to common airline thresholds that the printed battery label and the carrier's own wording matter.
This converter can help you do the arithmetic, but it does not replace airline, shipper, or manufacturer documentation.
Common voltage presets and travel-threshold interpretation
The calculator includes common voltage presets because the right voltage basis is the most common source of battery-capacity mistakes. A lithium-ion power-bank label is often based on internal cells around 3.7 V, while USB output checks may use 5 V, 9 V, 12 V, or 20 V after boost conversion. Larger battery banks often use 12 V, 24 V, or 48 V nominal system voltages.
Use those presets as starting points, not as substitutes for the product label. If a manufacturer prints both mAh and Wh, the printed Wh figure is usually the better source for travel or compliance checks. If you only have mAh and voltage, the converter shows the Wh result and a travel-threshold interpretation so near-limit packs are easier to spot before you rely on them.
The travel check is intentionally cautious. It flags the common under-100 Wh, 101-160 Wh, and above-160 Wh bands, but it cannot know whether a battery is installed in a device, spare, damaged, recalled, packed correctly, or subject to a stricter airline rule.
Home battery, solar, and EV examples
Larger battery systems are usually easier to compare in Wh or kWh. A 200 Ah battery at 48 V is 9,600 Wh, or 9.6 kWh, before usable-depth and efficiency assumptions. A 60 kWh EV pack at 400 V is about 150 Ah at the pack-voltage scale.
For solar storage and backup planning, the usable kWh figure is usually more useful than the nameplate kWh alone. Depth of discharge and conversion efficiency determine how much energy can realistically reach the load.
For EV charging, divide battery energy by charger power to estimate a rough charge time, then adjust for charging taper, losses, and the starting and target state of charge.
What this converter does not replace
This page is a unit and planning converter. It does not model lithium battery chemistry, state-of-charge curves, inverter surge rating, thermal limits, cable losses, charge taper, or battery management system cutoffs.
For safety, travel, engineering design, and financial decisions, confirm the result against the battery datasheet, device measurements, charger specifications, and the relevant rules for transport or installation.
The calculator also does not replace dedicated electricity cost, EV charging cost, or solar output calculators. Those pages handle tariff, solar-production, or vehicle-cost details that are intentionally outside this unit-conversion page.
Frequently asked questions
How do you convert mAh to Wh?
Divide mAh by 1,000 to get Ah, then multiply by nominal voltage. The formula is Wh = (mAh / 1000) x V. A 20,000 mAh battery at 3.7 V is about 74 Wh.
How do you convert Wh to mAh?
Multiply Wh by 1,000, then divide by voltage. The formula is mAh = (Wh x 1000) / V. Voltage must match the battery or output basis you are trying to describe.
How do you convert Ah to kWh?
Multiply amp-hours by voltage to get watt-hours, then divide by 1,000. For example, 100 Ah at 12 V is 1,200 Wh, which is 1.2 kWh.
Can you convert kWh to watts without time?
No. kWh is energy and watts are power. You need a runtime to convert energy into an average watt load, using watts = kWh x 1,000 / hours.
What is the difference between watts, Wh, and kWh?
Watts measure power at a moment in time. Wh and kWh measure accumulated energy. One kWh equals 1,000 Wh, and energy equals power multiplied by time.
Why does the converter ask for usable capacity and efficiency?
Nameplate battery capacity is not always the energy available to the load. Usable capacity, depth-of-discharge limits, inverter losses, charger losses, and cable losses can all reduce practical runtime.
Is Wh or mAh better for comparing power banks?
Wh is better for comparing power banks across different voltage bases because it measures stored energy directly. mAh is only comparable when the packs use the same nominal voltage basis.
Can this estimate EV battery charge time?
It can provide a rough energy divided by charger power estimate. Real EV charging time also depends on state of charge, charger limits, battery temperature, charging taper, and vehicle efficiency.
Should I use 3.7 V, 5 V, or USB-C output voltage for a power bank?
Use the voltage basis attached to the capacity rating you are converting. A power bank mAh label usually refers to internal cells around 3.7 V, while USB output voltage is after conversion. For delivered output, calculate stored Wh first and then apply the efficiency field instead of substituting 5 V, 9 V, or 20 V into the original mAh rating.
Why does a 20,000 mAh power bank not deliver 20,000 mAh at USB output?
The advertised mAh value usually describes the internal lithium-cell pack, not the regulated USB output after boost conversion. Convert the internal mAh rating to Wh first, then apply usable-capacity and efficiency losses. A 20,000 mAh pack at 3.7 V is about 74 Wh before losses, so the effective mAh at 5 V output will be lower.
What does the travel check in this battery energy converter mean?
The travel check compares the calculated watt-hours with common spare lithium-ion battery threshold bands. Under 100 Wh is usually the simplest band, 101-160 Wh commonly requires airline approval and quantity limits, and above 160 Wh is generally a serious compliance flag for passenger-aircraft spare batteries. Always use the printed battery label and the carrier's rules for the final decision.
