Battery Capacity Calculator

Battery capacity calculations rely on fundamental electrical relationships between voltage, current, and time. The primary formulas utilized by this calculator include:

1. Energy Storage (Watt-Hours):
Watt-hours (Wh) measure total energy capacity and are calculated by multiplying voltage (V) by ampere-hours (Ah):
Wh = V × Ah

2. Discharge Current (Amperes):
The C-rate defines the rate at which a battery is discharged relative to its maximum capacity. Discharge current (I) is found by multiplying ampere-hours by the C-rate:
I = Ah × C

3. Runtime to Full Capacity (Minutes):
Estimated runtime or charging duration can be derived directly from the C-rate using the formula:
Runtime = 60 / C

Imagine you have a 12-volt deep-cycle battery with a rating of 100 ampere-hours (Ah), and you are drawing power at a 0.5C rate. Let's walk through the math to find its total energy and discharge characteristics:

Step 1: Calculate Total Energy (Watt-Hours)
Multiply the voltage by the ampere-hours.
12 V × 100 Ah = 1,200 Wh
Your battery stores 1,200 watt-hours of electrical energy.

Step 2: Determine Discharge Current
Multiply the capacity by the 0.5C discharge rate.
100 Ah × 0.5C = 50 A
The device will draw 50 amperes of current.

Step 3: Calculate Runtime
Divide 60 minutes by the C-rate (0.5).
60 / 0.5 = 120 minutes
At a 0.5C discharge rate, the battery will fully discharge in 2 hours.

To maximize the lifespan and efficiency of your power systems, keep these professional tips in mind:

Respect Depth of Discharge (DoD): Regularly draining lead-acid batteries below 50% capacity drastically shortens their operational lifespan. Lithium-ion alternatives tolerate deeper discharges, but conservative usage still yields longevity.

Account for Temperature: Extreme cold reduces chemical reaction rates inside cells, temporarily lowering usable capacity, while excessive heat accelerates degradation.