Battery Bank Amp Hour Calculator
Size your battery bank by configuring batteries in series, parallel, or series-parallel combinations for optimal system capacity.
Advanced Bank Sizing
How to Use the Battery Bank Calculator
- Set Battery Specs: Enter the voltage and Ah rating of a single battery you plan to use.
- Choose Configuration: Increase Series batteries to match your system voltage (e.g., 2 batteries for 24V). Increase Parallel batteries to increase runtime.
- Define Load: Total all device Watts and the hours you need them to run.
- Adjust Safeties: Use standard efficiency (90%) and safe DoD (e.g., 50% for lead-acid).
- Analyze: The tool instantly shows if your bank is sufficient and how many total batteries you actually need.
Battery Bank Structure: Series vs Parallel
A battery bank is a collection of two or more batteries connected together for a single application. Understanding battery bank sizing requires knowing how connections affect electrical parameters.
1. Series Connection (Increases Voltage)
In a series connection, you connect the positive terminal of one battery to the negative of the next. This increases the total voltage but maintains the same Amp Hour capacity.
2. Parallel Connection (Increases Amp Hours)
In a parallel connection, you connect positive to positive and negative to negative. This increases the total Amp Hour capacity while keeping the voltage the same.
3. Series-Parallel (Increases Both)
Combining both methods allows you to build a system with both high voltage (e.g., 24V or 48V) and high capacity (hundreds of Ah).
Step-by-Step Multi-Battery Example
Consider a system with the following components:
- Single Battery: 12V, 100Ah
- Configuration: 2 Series (2S), 3 Parallel (3P)
- Load: 800W for 4 hours
Step 1: Calculate Bank Specs
Total Voltage = 12V × 2 = 24V
Total Capacity = 100Ah × 3 = 300Ah
Total Energy = 24V × 300Ah = 7200 Wh
Step 2: Apply System Loss (Formula)
Required Ah = (800W × 4h) / (24V × 0.9 × 0.5)
Required Ah = 3200 / 10.8 = 296.3 Ah
Result: Since 300Ah > 296.3Ah, the 6-battery bank is sufficient for the load.
Battery Bank Conversion Chart
Common multi-battery configurations using 12V 100Ah batteries:
| Batteries | Configuration | Voltage | Capacity | Energy (Wh) |
|---|---|---|---|---|
| 1 | Standalone | 12V | 100Ah | 1200Wh |
| 2 | Series | 24V | 100Ah | 2400Wh |
| 2 | Parallel | 12V | 200Ah | 2400Wh |
| 4 | Mixed (2S2P) | 24V | 200Ah | 4800Wh |
| 4 | Series (4S) | 48V | 100Ah | 4800Wh |
| 8 | Mixed (4S2P) | 48V | 200Ah | 9600Wh |
Note: Battery bank calculation always ensures Total Wh = Voltage × Amp Hours.
Frequently Asked Questions
Connecting batteries in parallel adds their Amp Hour capacities together. Connecting them in series increases voltage but the Amp Hour rating remains that of a single battery.
Neither is "better" overall. Series is used to reach target system voltages (like 24V for large inverters to reduce wire size), while parallel is used to increase runtime capacity.
No. You should never mix different voltages, capacities, or ages of batteries in a bank. This causes uneven charging, reduced lifespan, and potential safety hazards.
Multiply your target voltage by required Ah (found using our calculator) to get total Wh, then divide by the energy of a single battery (Voltage × Ah).
Most large off-grid systems prefer 48V (Series) to keep current low and efficiency high, while small RV or DIY setups often stick with 12V or 24V for simplicity.