What is ampere-hour (Ah) and milliampere-hour (mAh)?

Answer
Ampere-hour (Ah) and milliampere-hour (mAh) are units that describe a battery’s electrical charge capacity. They indicate how much current a battery can deliver over a certain period of time. Ah is commonly used for industrial and energy storage batteries, while mAh is mainly used for smaller batteries in electronics.

What does ampere-hour (Ah) mean?

An ampere-hour (Ah) is a measure of electrical charge. It represents:

Current (amperes) × time (hours)

In other words:
a battery rated at 1 Ah can theoretically deliver 1 ampere for 1 hour, or 2 amperes for 0.5 hours, and so on.

Example

If an application draws 20 amperes for 20 minutes:

20 minutes = 0.333 hours
Capacity used = 20 A × 0.333 h = 6.67 Ah

This means the battery supplies 6.67 ampere-hours during that period.

Why does the discharge time matter?

Battery capacity is always measured over a defined discharge period, also known as the C-rate.

For lead-acid batteries, like AGM batteries, the most common reference is:

C20 (20-hour rate)

This means:

The battery is discharged evenly over 20 hours
Until it reaches a final voltage (typically 10.5 V for a 12 V lead-acid battery)
The total delivered charge is measured in Ah

Other common reference times

C6 → used for applications with higher daily loads
C100 → used for long-duration, low-current applications

Important:
A higher Ah rating at a longer discharge time does not mean the battery delivers the same capacity at higher currents.

This is why some batteries may appear to have a higher Ah rating when measured at longer discharge times.

What does milliampere-hour (mAh) mean?

A milliampere-hour (mAh) is the same unit as Ah, but scaled down:

1 Ah = 1000 mAh

mAh is typically used for small batteries in:

portable electronics
sensors
consumer devices

Example

A 2000 mAh battery can theoretically deliver:

2000 milliamperes (2 A) for 1 hour, or
1000 milliamperes for 2 hours

A higher mAh rating indicates more stored charge, not higher power or speed.

Ah vs mAh: what is the difference?

Unit	Meaning	Typical use
Ah	Ampere-hour	Industrial batteries, energy storage, UPS systems
mAh	Milliampere-hour	Small batteries, electronics
Relation	1 Ah = 1000 mAh	Same unit, different scale

Important notes when comparing battery capacity

Ah and mAh describe charge, not energy
Energy depends on voltage as well (Wh = Ah × V)
Capacity varies with:
- discharge rate
- temperature
- battery chemistry
Comparing Ah values only makes sense when:
- the same voltage
- the same discharge rate
- the same battery technology are used

When does understanding Ah and mAh matter most?

This is especially important for:

Battery sizing and system design
Energy storage systems
Backup power applications
Charging infrastructure
Comparing battery specifications

In short

Ah and mAh indicate how much electrical charge a battery can deliver over time.
Ah is used for larger batteries, mAh for smaller ones. Both describe the same principle.

Not sure how much battery capacity your application requires?
Our specialists can help calculate the right battery size based on load, voltage and usage profile.