Battery Bank Capacity Calculator
Battery Bank Capacity Calculator helps you size a complete battery bank made of multiple batteries. It ensures your system delivers reliable backup power without under-sizing or over-spending.
Bank Sizing Tool
How to Use Battery Bank Capacity Calculator
Follow these simple steps to size your battery bank correctly:
- Step 1: Enter Total Load (Watts) - Add the wattage of all devices. Example: Lights + Fan + TV = Total watts.
- Step 2: Enter Backup Time (Hours) - Define how long you need power.
- Step 3: Enter System Voltage (V) - Choose system voltage (12V, 24V, 48V).
- Step 4: Enter Depth of Discharge (DoD) - Lead-acid: 50%, Lithium: 80–90%.
- Step 5: Enter Efficiency (%) - Typical: 85%–95%.
- Step 6: Enter Single Battery Specs - Battery Voltage (e.g., 12V) and Battery Capacity (Ah).
- Step 7: Click Calculate - The calculator gives total required capacity (Ah), number of batteries needed, and configuration.
How to Calculate Battery Bank Capacity
To determine the size of a battery bank, you need to factor in the electrical load, the desired runtime, and the losses associated with discharge depth and system efficiency.
The Formula
Step-by-Step Example
Given: Load = 800W, Backup Time = 5 hours, System Voltage = 24V, DoD = 50% (0.5), Efficiency = 90% (0.9).
1. Calculate Energy:
800W × 5 hours = 4000 Wh
2. Multiply Voltage × DoD × Efficiency:
24V × 0.5 × 0.9 = 10.8
3. Divide:
4000 ÷ 10.8 = 370.37 Ah
Final Required Capacity: ≈ 371 Ah at 24V
Calculate Number of Batteries
Once you have the total required capacity, you can determine how many individual batteries (e.g., 12V 200Ah) make up that bank.
Example Battery: 12V, 200Ah battery
Step 1: Batteries in Series (to reach system voltage)
System Voltage ÷ Battery
Voltage = 24 ÷ 12 = 2 batteries in series
Step 2: Capacity of One Series String
Series keeps Ah same → 200Ah
Step 3: Parallel Strings Needed
Required Ah ÷ Battery Ah = 371 ÷ 200 = 1.85 →
2 strings
Step 4: Total Batteries Required
Series × Parallel = 2 × 2 = 4 batteries
total
Final Setup: 2 batteries in series × 2 parallel strings = 4 batteries total.
Battery Bank Capacity Conversion Chart
Assuming 50% DoD and 90% efficiency. Battery count includes proper series + parallel configuration using 12V 200Ah batteries.
| Load | Time | System Voltage | Required Ah | Batteries (12V 200Ah) |
|---|---|---|---|---|
| 300W | 5H | 12V | 278 Ah | 2 batteries |
| 500W | 5H | 12V | 463 Ah | 3 batteries |
| 800W | 5H | 24V | 371 Ah | 4 batteries |
| 1000W | 6H | 24V | 463 Ah | 4 batteries |
| 1500W | 5H | 48V | 347 Ah | 8 batteries |
| 2000W | 4H | 48V | 370 Ah | 8 batteries |
Frequently Asked Questions (FAQs)
A single battery cannot meet higher voltage or capacity needs. Multiple batteries create a complete system that can scale power for larger applications.
Series connection increases the total voltage of the bank while keeping the Amp-hour (Ah) capacity the same as a single battery.
Parallel connection increases the total Amp-hour capacity of the bank while keeping the system voltage the same.
Calculate the required Ah for your load, then divide by single battery Ah and adjust for system voltage to find the total battery count.
No. Always use identical batteries (same voltage, same Ah, same brand, same age) for safety and optimal performance.