Battery Capacity Ah vs Wh: Which Number Matters on an E-Bike?

Ah tells you electrical charge capacity. Wh tells you energy capacity. If you want to compare how much energy two e-bike batteries store, watt-hours are usually the more useful number—especially when the batteries use different voltages.

The relationship is simple:

Wh = V × Ah

So a 36V 15Ah battery stores 540Wh of nominal energy, while a 48V 15Ah battery stores 720Wh. Both say 15Ah, but they are not equal-capacity batteries.

The quickest rules to remember are:

Same voltage: Ah can be useful for comparing capacity.
Different voltage: compare Wh.
Estimating range: start with Wh, then consider energy consumption.
Looking at motor power: W and Wh are different measurements.
Replacing a battery: capacity alone does not prove compatibility.

Ah vs Wh: What Each Number Actually Tells You

Battery labels can put 36V, 48V, 14Ah, 500Wh and motor wattage close together, which makes the numbers look more interchangeable than they really are.

They answer different questions.

Ah: electrical charge capacity

Amp-hours (Ah) measure electrical charge.

Bosch describes amp-hours in e-bike batteries as the unit for the electrical charge contained in the battery.

Ah is useful when you already know the battery voltage.

For example, if you are comparing two compatible 48V batteries, a 15Ah pack has more charge capacity than a 10Ah pack and will also have more nominal energy.

The problem is using Ah without voltage.

A 15Ah rating does not tell you a battery’s energy capacity by itself.

Wh: stored energy

Watt-hours (Wh) measure energy.

Bosch describes Wh as the energy content of an e-bike battery and identifies it as relevant to available range.

Because Wh incorporates both voltage and Ah, it gives you a much cleaner answer to:

“Which of these batteries stores more energy?”

For most cross-voltage battery comparisons, that is the number to check first.

What about V, A and W?

Keep these separate:

V — volts: electrical voltage.
A — amps: electrical current at a given moment.
Ah — amp-hours: electrical charge capacity.
W — watts: power, or the rate at which energy is transferred.
Wh — watt-hours: an amount of energy.

NIST defines the watt as a unit of power equal to one joule per second, while a watt-hour is an energy unit equal to 3,600 joules.

That distinction becomes important when you see something like a 750W motor beside a 750Wh battery. The identical-looking numbers do not describe the same thing.

How to Convert Amp-Hours to Watt-Hours

If the battery gives you voltage and Ah but not Wh, use:

Wh = V × Ah

You only need three steps:

Find the battery’s rated voltage.
Find its Ah rating.
Multiply them.

For a 36V 14Ah battery:

36 × 14 = 504Wh

This matches a real Shimano specification. Shimano lists its BT-E8010-A battery at 36V, 14Ah and 504Wh.

That makes the formula useful for more than textbook math: you can use it to check and compare specifications while shopping.

Which voltage should you use?

Use the rated or nominal voltage associated with the battery’s Ah specification.

In other words, if the manufacturer’s specification pairs 36V with 14Ah, use those matching figures.

Do not mix values from different specifications or substitute another voltage simply because the battery voltage changes during charging or discharge. You are trying to reproduce the rated capacity comparison, not calculate energy from mismatched numbers.

Converting Wh back to Ah

Reverse the formula:

Ah = Wh ÷ V

For example:

672Wh ÷ 48V = 14Ah

Voltage is still required. There is no meaningful universal conversion between Ah and Wh without it.

Two 15Ah Batteries Can Store Very Different Amounts of Energy

This is the point that causes many bad battery comparisons.

Consider two hypothetical e-bike batteries:

Battery	Rating	Energy
A	36V, 15Ah	540Wh
B	48V, 15Ah	720Wh

Looking only at Ah, they appear identical.

Looking at energy, they clearly are not.

Battery B stores 180Wh more nominal energy, which is about 33% more than Battery A.

That is why “15Ah battery” is incomplete information when you are comparing packs with different voltages.

When can you safely compare Ah?

Use Ah as a shortcut when the voltage is the same.

For example:

48V 10Ah = 480Wh
48V 15Ah = 720Wh

Because voltage is unchanged, the higher-Ah battery also has proportionally more nominal energy.

Once voltage changes, stop comparing Ah alone and switch to Wh.

More energy does not mean the battery is compatible

Suppose your bike uses a 36V battery and you find a 48V pack with a much higher Wh rating.

That does not mean the 48V pack is a better replacement.

Capacity comparison and compatibility are two separate questions.

A replacement may also need to match requirements involving:

system voltage;
controller;
connectors;
physical mounting and fit;
battery management system;
charger;
manufacturer specifications.

For safety, the U.S. Consumer Product Safety Commission advises using replacement or secondary battery packs that have been tested and approved to work with the device and confirmed suitable by its manufacturer.

Practical rule: use Wh to decide which battery stores more energy. Use the bike manufacturer’s compatibility information to decide which battery belongs on the bike.

For E-Bike Range, Should You Look at Ah or Wh?

Start with Wh.

Range depends on how much energy the battery can provide and how quickly the bike uses that energy. Because Ah leaves voltage out of the picture, it is a poor standalone metric for comparing range across batteries with different voltages.

Consider:

36V × 20Ah = 720Wh

and

48V × 15Ah = 720Wh

The first pack has 20Ah and the second only 15Ah, yet both have the same nominal energy rating.

So the statement “more Ah always means more range” is incomplete.

It works reasonably as a shortcut only when voltage and the rest of the comparison remain equivalent.

Turning Wh into a rough range estimate

A useful planning relationship is:

Estimated range ≈ available Wh ÷ average Wh per mile

For a clearly hypothetical example, imagine a ride averaging 18Wh per mile with 672Wh available for the calculation:

672 ÷ 18 ≈ 37 miles

That does not mean every 672Wh e-bike will travel 37 miles.

Actual consumption changes with factors such as:

assistance level;
speed;
rider and cargo weight;
hills;
wind;
temperature;
tires and tire pressure;
stop-and-start riding.

Two riders can therefore get different distances from batteries with the same Wh rating.

What this means when shopping: use Wh to compare energy capacity. Do not treat Wh as a guaranteed mileage figure.

For detailed distance planning, move from this capacity comparison to a full e-bike range estimate that accounts for real Wh-per-mile consumption.

A 750W Motor and a 750Wh Battery Are Not the Same Thing

This is one of the easiest specification mistakes to make.

A listing might show:

Motor: 750W
Battery: 720Wh

Those numbers answer different questions.

Watts (W) describe power: the rate at which energy is transferred or used.

Watt-hours (Wh) describe energy: how much energy is available over time.

So there is no rule saying:

750W motor = 750Wh battery

A motor’s watt rating does not tell you the battery’s energy capacity, and a battery’s Wh rating does not by itself tell you everything about the power it can safely deliver.

For battery-to-bike compatibility, other specifications can matter, including voltage, current capability, controller requirements and battery-management limits.

Which specification should you check?

Your question	Check first
Which battery stores more energy?	Wh
Which same-voltage battery has more charge capacity?	Ah
How much power is involved?	W
What voltage system does the bike use?	V
How far might the bike travel?	Wh + energy consumption
Will a replacement battery work?	Manufacturer compatibility specs

That decision is more useful than searching for the single “best” battery number. There isn’t one metric that answers every battery question.

Does the Capacity Printed on the Battery Equal What You Will Actually Get?

Not necessarily.

The number on the label is primarily a rated or nominal specification. It gives you a standardized way to describe and compare the battery.

Measured or practically available energy is a different question.

Battery condition and operating circumstances can affect real-world performance. Shimano, for example, publishes battery capacity-retention information after repeated charging cycles and separately discusses low-temperature performance, illustrating why a battery’s behavior over time and under different conditions should not be reduced to one permanent real-world number.

That is why you should avoid rules such as:

“Every 500Wh battery gives exactly 500Wh in every ride.”

You should also avoid assigning one universal “usable capacity percentage” to every e-bike battery. Manufacturers, battery designs, operating limits, test methods and battery condition differ.

A simple battery-label sanity check

You can still use the Ah/Wh formula to check whether a specification makes mathematical sense.

Suppose a battery is advertised as:

48V — 14Ah — 672Wh

Check it:

48 × 14 = 672Wh

The numbers are internally consistent.

If instead the listed Wh figure differs substantially from the result, use this sequence:

Confirm that you copied the voltage and Ah correctly.
Check the manufacturer’s official specification.
Make sure the figures refer to the same battery version.
Investigate further if the difference remains unexplained.

This is a sanity check, not a battery-health test and not a fraud detector.

A mismatch does not automatically prove that the battery is counterfeit, defective or unsafe.

Likewise, matching numbers do not prove that an older battery still delivers its original capacity.

If a battery’s real-world performance has deteriorated, that is a battery-health question rather than an Ah-vs-Wh calculation.

The E-Bike Battery Rule Worth Remembering

When you read a battery specification, work through it in this order:

1. Check the voltage.
It gives the Ah rating its energy context.

2. Check Ah.
It tells you charge capacity and is useful for same-voltage comparisons.

3. Check or calculate Wh.
Use Wh = V × Ah to compare stored energy.

4. Match the number to your actual question.
Range, motor power, stored energy and compatibility require different information.

5. Check compatibility separately.
A battery with more Wh is not automatically suitable for your bike.

If you remember only one comparison rule, make it this:

Same voltage? Ah can help. Different voltage? Compare Wh.

That one check prevents most of the confusion behind e-bike battery capacity specifications.