Battery Bank Calculator
Series/parallel bank voltage, Ah, and Wh.
Battery Bank Calculator
A battery bank combines multiple modules in series and parallel to reach the system voltage and amp-hour capacity your inverter and loads need. The inputs are one battery’s Ah and voltage, plus how many strings you wire in series and how many in parallel.
Series connections add voltage; parallel connections add amp-hours while voltage stays the same. Getting this wrong means a bank that does not match your charge controller or inverter, uneven charging, or unsafe string design. This calculator totals bank volts, Ah, and Wh from your module count.
Use it when you have chosen a commercial battery size (e.g. 12 V 100 Ah) and need to see what 2S2P or 4S2P delivers. Pair with battery capacity sizing to know how much energy you need, then use this tool to translate that into a physical layout.
How this calculator works
- Enter single battery amp-hours (Ah) and nominal voltage (V) from the module datasheet.
- Enter series count: batteries wired positive-to-negative in a string to multiply voltage.
- Enter parallel count: identical strings connected in parallel to multiply amp-hours.
- Bank voltage = single battery V × series count.
- Bank Ah = single battery Ah × parallel count. Bank Wh = bank V × bank Ah.
Core bank relationships
Bank V = single V × series | Bank Ah = single Ah × parallel | Bank Wh = Bank V × Bank Ah
Series strings raise voltage so the bank matches 12, 24, or 48 V equipment. Parallel strings raise capacity (Ah) without changing voltage. Total energy in watt-hours is always voltage times amp-hours at the bank terminals—use Wh to compare banks even when Ah and V differ between designs.
Formulas used by this tool
- Bank voltage = single battery volts × series count.
- Bank Ah = single battery Ah × parallel count.
- Bank Wh = bank volts × bank Ah.
Worked example: 2S2P with 12 V 100 Ah
You have 12 V, 100 Ah modules and plan two in series and two parallel strings (four batteries total).
- Series count = 2 → bank voltage = 12 V × 2 = 24 V nominal.
- Parallel count = 2 → bank Ah = 100 Ah × 2 = 200 Ah.
- Bank Wh = 24 V × 200 Ah = 4,800 Wh nameplate.
- Total modules = series × parallel = 4 batteries—verify fusing, cable size, and BMS per manufacturer for this configuration.
Practical tips
- Use identical batteries in each string—mixed ages or chemistries cause imbalance.
- Series raises voltage only; parallel raises Ah only—Wh scales with both.
- Check inverter and charge controller max voltage before adding series cells.
- Many lithium packs include an integrated BMS; DIY lead-acid banks need proper fusing per string.
- After sizing Wh with capacity tools, adjust series/parallel until bank V matches your system architecture.
Frequently asked questions
What is series vs parallel?
Series connects positive of one battery to negative of the next, adding voltage. Parallel connects all positives together and all negatives together, adding amp-hours while voltage stays the same. A 2S2P bank uses two series pairs wired in parallel.
Why does bank Wh matter more than Ah alone?
Amp-hours depend on voltage. 100 Ah at 12 V is 1,200 Wh; 100 Ah at 48 V is 4,800 Wh. Watt-hours let you compare total stored energy across different bank voltages and module layouts.
How many batteries do I need total?
Multiply series count × parallel count. A 4S2P layout uses eight modules. The calculator outputs bank totals; you supply the counts based on your wiring plan.
Can I mix 12 V and 24 V batteries?
No. All modules in a bank should be the same model and state of health. Mixed voltages or capacities cause uneven charge, damaged cells, and safety risks. Build strings from matched batteries only.
Does this include usable capacity or DoD?
No. Results are nameplate V, Ah, and Wh. Usable energy depends on chemistry and depth of discharge—use the battery runtime or capacity calculators for DoD and load planning.
How do I pick series and parallel counts?
Choose series to reach system voltage (e.g. four 12 V batteries in series for 48 V). Choose parallel to reach required Ah after capacity sizing. Iterate until bank Wh meets your load and autonomy targets within equipment limits.
Related guides
Related calculators
Continue sizing with a related tool.