What's Ah In Battery - Battery Ah Meaning

What's Ah in Battery - Ah Battery Meaning

From time to time, people ask us what does Ah mean on a battery - well, Ah or Amp-Hours is a unit of capacity that describes how much current a battery can provide under certain conditions.

While some batteries feature capacity in hundreds and thousands of Amp-Hours, smaller batteries feature capacities that are measured in milli-Amp-Hours (mAh) or even micro-Amp-Hours (μAh).

Updated: October 30, 2024.

What Does Ah Mean on a Battery: Battery Capacity Definition

Generally, the battery capacity is a unit of measure that describes how many Amps (A) or milli-Amps (mA) the battery can provide for 20 hours before its voltage drops below a certain level - that "certain level" is commonly labeled as a cut-off voltage or drop-off voltage.

This definition of the battery capacity is usually given for lead-acid batteries, although some manufacturers provide capacities for other discharge rates, for example, for 1h, 2h, 3h, 5h, 10h, etc.

The capacity of wet/flooded, AGM, and Gel-Cell 12V lead-acid batteries is determined by how many Amps can a new, fully charged 12V battery deliver for 20 hours without its voltage falling below 10.5V at 77-80°F (25-27°C).

Note: Draining the rechargeable battery below cut-off voltage could cause permanent damage to the battery - cut-off voltage primarily depends on the battery chemistry, but also on the battery construction and design, since it is not the same to fully discharge starting or deep-cycle lead-acid battery.

Since rechargeable lithium batteries don't suffer from the capacity decrease like lead-acid batteries when they are discharged with 0.5-1.0C or stronger currents, many manufacturers of lithium batteries provide 1h capacity of their batteries, which is "almost" the same as 20h capacity of the lithium batteries.

As one can see, the capacity of the battery depends on the exact chemistry and the battery construction and hence, type.

For example, two batteries may be based on the same chemistry, but one is deep cycle battery, optimized for low-drain applications (high capacity, low discharge current), while another battery is starting/cranking, and it is optimized for high-drain applications (lower capacity, higher discharge current).

The "quality" of such batteries for a certain application should not be based only on the capacity - deep cycle battery despite having larger capacity does NOT perform well in high current applications.

How to Calculate the Capacity (Ah) of a Battery

If you have a battery that is able to provide, for example, 5 Amps for 20 hours constantly from the 100% SoC (State of Charge) or 0% DoD (Depth or Discharge) down to 0% SoC or 100% DoD, then that battery has the capacity of:

Capacity (Ah) = I(A) * t(h) = 5A * 20h = 100Ah

So, the capacity of the battery in this example is 100Ah (Amp-hours).

Similarly, if you have 12.8V battery that is able to store 1280Wh of energy, then the capacity of such battery is:

Capacity (Ah) = E(Wh) / U(V) = 1280 Wh / 12.8 V = 100 Wh/V = 100 VAh/V = 100Ah

Note: Energy is usually given in Joules, but energy stored in batteries is mostly given in Watt-hours, which is actually Volt-Amp-hours.

Battery Capacity (Ah) in Different Battery Chemistries

The following table lists some of the most popular chemistries commonly found at cylindrical batteries - the data are given for the cylindrical AA batteries.

Chemistry	Common Name	Rechargeable	Typical Capacity (mAh)	Voltage (V)
Zinc Carbon	R6, 15D	No	600 - 1600	1.5
Alkaline	LR6, 15A	No (Mostly No)	1800 - 2700	1.5
Li-FeS2	FR6, 15LF	No	2700 - 3300	1.5 (1.8 max)
Li-ion	14500	Yes	600 - 2000+	3.6 - 3.7
LiFePO4	IFR14500	Yes	500-750	3.2
Li-SOCl2	(14505)	No	2400-2700	3.5-3.6
Li-MnO2	CR AA	No	~2000	3.0
Lithium	-	Yes	1000-2000+	1.5
NiCd	KR6, 1.2K2	Yes	600 - 1200	1.2
NiMH	HR6, 1.2H2	Yes	700 - 2800	1.2
NiOOH	-	No	2200 - 2700	1.5 (1.7 max)
NiZn	ZR6	Yes	1500 - 1800	1.6 - 1.65

As one can see, although the batteries in the table share the same physical dimensions, their electrical characteristics differ significantly.

Such differences exist in all battery sizes, from small button/coin-cell batteries to large automotive/light industrial batteries.

The Difference Between Amps, Ohms, and Volts

Amps, ohms, and volts are units used to measure different aspects of electricity. Here’s how they differ:

• Amps (Amperes): Measure the flow of electric current. Current refers to the rate at which electric charges pass through a point in a circuit. Think of it like water flowing through a pipe—the stronger the current, the more electricity is flowing. Amps tell you how much electricity is moving.
• Ohms: Measure electrical resistance. Resistance determines how much a material resists the flow of electric current. High resistance means it's harder for electricity to pass through. Think of it as a narrowing in a pipe that restricts water flow—the higher the resistance, the more restricted the current is. Ohms tell you how much a material limits electrical flow.
• Volts (Voltage): Measure electric potential difference (or electric pressure). Voltage is what "pushes" the current through the circuit. Imagine it as water pressure in a pipe - the higher the pressure, the more force there is to push the water through. Volts tell you the "push" driving the electric current.

Is a Higher Capacity (Ah) Battery Better?

A higher-capacity battery (measured in amp-hours, or Ah) can be "better" in terms of providing a longer runtime before recharging, but whether it’s the right choice depends on your needs and device specifications.

Benefits of Higher Ah Batteries

• Longer Runtime: A higher Ah rating means the battery can supply a device with power for a longer period. This is ideal for applications where a longer runtime is essential, such as in electric vehicles, backup systems, or tools.
• Efficiency with High-Drain Devices: For devices that consume a lot of energy (like power tools), a higher-capacity battery can handle the load more effectively, avoiding frequent recharges.
• Reduced Maintenance or Replacement Frequency: Batteries with a higher capacity generally don’t need recharging or replacement as often, potentially lowering long-term maintenance.

Considerations

• Weight and Size: Higher-capacity batteries are often larger and heavier, which might be impractical or inconvenient for some applications (like portable electronics or small devices).
• Cost: Higher Ah batteries are usually more expensive due to the extra materials and capabilities.
• Compatibility: Not all devices are designed to work with high-capacity batteries, as they may require specific voltage or charging settings. It’s essential to check if your device can handle a larger battery without impacting performance or safety.

A higher-capacity battery is generally "better" for devices requiring extended power but is most beneficial when the increased runtime outweighs the downsides in size, weight, and cost.

Also, if the application requires starting/cranking battery, even a smaller starting battery with high Cold Cranking Amps/Marine Cranking Amps (CCA/MCA) rating will be better than larger deep-cycle high-capacity battery with lower CCA/MCA rating.

If You are looking for the battery capacity of a certain battery, feel free to use the Search: write down the battery size, click Search, and the system will find it for You, assuming that the battery exists on the Battery Equivalents site.