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Battery Calculator – Estimate Battery Life and Run Time

Battery Calculator

Estimate runtime and energy storage requirements for your electronic devices and power systems.

Total Amp-hours of the battery. For mAh, divide by 1000.
Please enter a positive capacity.
Nominal voltage of the battery system.
Power consumption of the connected devices.
Load must be greater than zero.
Safe discharge level (Lead-acid: ~50%, Lithium: ~80-95%).
Depth must be between 1 and 100.
Energy loss during conversion (typically 85-95%).
Efficiency must be between 1 and 100.
Estimated Run Time 14.40 Hours
Total Battery Energy (Wh) 1200 Wh
Usable Battery Energy (Wh) 864 Wh
Current Draw (Amps) 5.00 A

Energy Distribution (Wh)

Comparison of Total Storage vs. Usable Storage after losses.

Typical Run Times for this Battery

Load (W) Run Time (100% DoD) Run Time (Your DoD) Daily Energy Use

Table shows estimated performance at various power levels.

What is a Battery Calculator?

A Battery Calculator is an essential tool for engineers, hobbyists, and solar enthusiasts designed to determine how long a specific battery system can power a given load. Whether you are building an off-grid solar system, sizing a UPS for your home office, or calculating the flight time of a drone, understanding the relationship between capacity, voltage, and discharge rates is critical.

Using a Battery Calculator helps prevent "deep discharge" damage to expensive battery banks. By inputting variables like Amp-hours (Ah) and Depth of Discharge (DoD), users can ensure their systems remain within safe operational limits. Common misconceptions include assuming a battery provides 100% of its rated capacity until it hits 0V; in reality, voltage drops during discharge, and efficiency losses in inverters further reduce available run time.

Battery Calculator Formula and Mathematical Explanation

The core mathematics behind a Battery Calculator involves converting electrical capacity into energy units and then dividing by the consumption rate. Here is the step-by-step derivation:

  1. Total Energy (Wh): Capacity (Ah) × Voltage (V)
  2. Usable Energy (Wh): Total Energy × (DoD / 100) × (Efficiency / 100)
  3. Run Time (Hours): Usable Energy (Wh) / Load (W)
Variable Meaning Unit Typical Range
Capacity (C) Quantity of charge stored Ah / mAh 1Ah to 1000Ah
Voltage (V) Electrical potential Volts (V) 3.7V to 48V
Load (P) Power consumption Watts (W) 1W to 5000W
DoD Depth of Discharge Percentage (%) 50% to 95%

Practical Examples (Real-World Use Cases)

Example 1: Marine Deep Cycle Battery
A boat owner uses a 100Ah 12V Lead-Acid battery. They want to power a 40W fridge. Lead-acid batteries should only be discharged 50%. Using the Battery Calculator: (100Ah * 12V * 0.50) / 40W = 15 Hours. With a 90% inverter efficiency, the real run time is 13.5 hours.

Example 2: Portable Power Station (Lithium)
A camper has a 200Ah 12V Lithium (LiFePO4) battery. They run a laptop (60W) and LED lights (20W) for a total load of 80W. Lithium allows 90% DoD. Calculation: (200Ah * 12V * 0.90) / 80W = 27 Hours of continuous use.

How to Use This Battery Calculator

1. Enter Capacity: Look at your battery label for the "Ah" rating. If it says 5000mAh, enter 5 in this Battery Calculator.

2. Select Voltage: Standard car/solar batteries are 12V. E-bikes often use 36V or 48V.

3. Define Load: Add up the wattage of all devices. A router might be 10W, while a space heater is 1500W.

4. Adjust DoD: Be conservative. If using Lead-Acid, set to 50%. For Lithium, 80-90% is safe.

5. Check Results: Review the chart to see how much energy is "wasted" vs. "usable" to optimize your setup.

Key Factors That Affect Battery Calculator Results

  • Temperature: Cold environments significantly reduce chemical activity, lowering the effective capacity shown in any Battery Calculator.
  • Peukert's Law: High discharge rates (pulling energy fast) reduce total available capacity compared to slow discharge rates.
  • Battery Age: Over time, internal resistance increases and capacity fades. An old 100Ah battery might only behave like an 80Ah battery.
  • Wiring Resistance: Thin wires between the battery and the load cause voltage drops, leading to efficiency losses.
  • Self-Discharge: Batteries lose charge naturally over time, even with no load connected.
  • Charge Controller Settings: If the charger doesn't fully saturate the battery, the initial capacity for the Battery Calculator will be lower than rated.

Frequently Asked Questions (FAQ)

Can I discharge my battery to 0%?

Technically yes, but it will permanently damage most battery chemistries. Lead-acid batteries should never go below 50% for longevity.

What is the difference between Ah and Wh?

Ah (Amp-hours) measures charge, while Wh (Watt-hours) measures total energy. Wh = Ah × Voltage.

Does this Battery Calculator account for Peukert's Law?

This calculator uses a linear estimation. For very high discharge rates (like starting an engine), the runtime may be shorter than calculated.

Why is my inverter efficiency not 100%?

Inverters generate heat during the DC to AC conversion process. This heat is lost energy, typically accounting for 5-15% of the total capacity.

How do I calculate for parallel battery banks?

When batteries are in parallel, the voltage stays the same, but you add the Ah together. Two 100Ah batteries in parallel equal 200Ah.

What about series battery banks?

In series, the Ah stays the same, but the voltage increases. Two 12V 100Ah batteries in series equal a 24V 100Ah bank.

Is LFP better than Lead Acid?

Yes, Lithium Iron Phosphate (LiFePO4) allows for higher DoD (up to 95%) and more cycles, though the initial cost is higher.

How often should I check my battery health?

It is recommended to check voltage levels monthly and perform a capacity test annually to update your Battery Calculator inputs.

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