Battery Voltage Calculator

Ever wondered why your battery doesn’t give the same voltage under load? Our Battery Voltage Calculator helps you find the true terminal voltage, power loss, and efficiency in seconds. You’ll know exactly how much voltage your battery delivers when current flows through it.

We built this calculator so anyone from a student to a technician can calculate battery voltage quickly, with zero confusion. It’s fast, accurate, and 100% free to use.

What Is Battery Voltage?

Battery voltage is the electric potential difference between the battery’s terminals. It tells you how much energy per charge the battery can supply. When no current flows, it’s called the Open Circuit Voltage (OCV). When current flows, voltage drops slightly due to the internal resistance of the battery.

This drop is why your car or phone battery might show a lower voltage when running.

How Do You Calculate Battery Voltage?

You can calculate the terminal voltage using a simple formula:

Vterminal = Eocv − I × Rint

Where:

• Vterminal = Terminal voltage (Volts)
• Eocv = Open Circuit Voltage (Volts)
• I = Current drawn (Amperes)
• Rint = Internal resistance (Ohms)

This formula is widely used in electrical and physics calculations. It shows how internal resistance causes a small voltage loss when current flows.

Example:

If a battery has

Eocv = 3.7 V,

I = 5 A, and

Rint = 0.05 Ω,

Then:

Vterminal = 3.7 − (5 × 0.05) = 3.45 V

So, under load, your 3.7V battery delivers 3.45V to the device.

How to Use the Battery Voltage Calculator

Using our calculator is super simple:

1. Enter your Open Circuit Voltage (Eocv).
2. Enter the Current (I) in amperes.
3. Enter the Internal Resistance (Rint) in ohms.
4. Choose your desired units (V, mV, or kV).
5. Click Calculate to get your Terminal Voltage, Power Loss, and Efficiency instantly.

The calculator also shows every calculation step so you can learn how it works while using it.

Understanding the Results

Once you hit Calculate, you’ll see:

• Voltage Drop (I × Rint): This is the small voltage lost inside the battery.
• Terminal Voltage (Eocv − I × Rint): The actual voltage available to your load.
• Power Loss (I × Voltage Drop): Energy wasted as heat inside the battery.
• Efficiency: How much of the original voltage remains useful.

So, if you see low efficiency, it might be time to check your battery health or internal resistance.

Final Verdict

Our Battery Voltage Calculator makes understanding battery behavior simple. You can see how voltage changes with current and resistance in real time.

It’s more than just a formula it’s a learning tool that helps you see electricity in action.

Try it once, and you’ll never have to guess your battery voltage again.

FAQs

What is open-circuit voltage (OCV)?

It’s the voltage of a battery when no current flows basically, the pure battery voltage.

Why does voltage drop when a battery delivers current?

Because internal resistance causes a small loss, turning some energy into heat.

How do I find internal resistance?

You can measure it by checking the voltage difference under load and dividing it by the current.

What’s a good battery efficiency?

A healthy battery usually operates above 90% efficiency under normal load.

Can I use this for any battery type?

Yes! It works for Li-ion, lead-acid, NiMH, and any other rechargeable or disposable cell.