Amps to Amp-Hours

Understanding Battery Capacity: Amps vs. Amp-Hours

In the world of electronics, solar energy, and automotive mechanics, understanding how electricity is stored is just as important as understanding how it flows. While "Amps" measure the flow of current right now, "Amp-Hours" (Ah) measure the total amount of charge stored or consumed over time. Our Ampere to Ampere-Hour Calculator bridges this gap, helping you size batteries and estimate runtimes with precision.

The Core Formula: Ah = I × t

The relationship between current, time, and capacity is linear and straightforward:
$$Ah = Amps \times Hours$$
- Ah (Ampere-Hour): The unit of electric charge (battery capacity).
- Amps (Current): The rate of electron flow.
- Hours (Time): The duration the current flows.

Example:
If a device draws 5 Amps and runs for 10 hours:
$5 \text{ Amps} \times 10 \text{ Hours} = 50 \text{ Ah}$.
This means you need a battery with at least 50Ah capacity to power that device for the full duration.

What Does an Amp-Hour Really Mean?

Think of a battery like a water tank.
- Amps are the speed of water flowing out of the pipe (Gallons per minute).
- Amp-Hours are the total gallons in the tank.
A 100Ah battery can theoretically deliver:
- 1 Amp for 100 Hours.
- 10 Amps for 10 Hours.
- 100 Amps for 1 Hour.
Mathematically, the total charge is the same ($1 \times 100 = 100 \times 1$). However, in the real world, chemistry gets in the way.

Real-World Constraints: Peukert's Law

It is important to note that lead-acid batteries (and to a lesser extent, Lithium) adhere to Peukert's Law. This law states that as the rate of discharge increases, the battery's available capacity decreases.
- If you drain that 100Ah battery at 1 Amp, you might get the full 100 hours.
- If you drain it at 100 Amps, you won't get 1 hour; you might only get 30 minutes.
For this reason, calculations from this tool represent the "Nominal" or "Theoretical" capacity. When sizing a battery bank for solar or heavy loads, experts recommend adding a safety margin of 20-50%.

Amp-Hours vs. Watt-Hours (Wh)

Ah tells you the charge capacity, but not the total energy. To know the energy, you must factor in voltage.
$$Watt-Hours (Wh) = Amp-Hours (Ah) \times Volts (V)$$
- A 100Ah battery at 12V = 1200 Wh.
- A 100Ah battery at 24V = 2400 Wh.
Even though both are "100Ah," the 24V battery holds twice the energy. Always check the system voltage when comparing batteries.

Applications

1. Solar Systems: Estimating how many hours your battery bank can run your appliances at night.
2. RVs and Boats: Calculating "House Bank" size to keep the lights and fridge running while anchored.
3. Phone Chargers: Power banks are often rated in milliamp-hours (mAh). $1 Ah = 1000 mAh$. A 20,000mAh power bank is 20Ah.