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Battery bank series & parallel calculator
Work out the voltage, amp-hours and total energy of a battery bank wired in series, parallel or series-parallel, with wiring tips for matched batteries.
Results
| Bank voltage | 25.6 V |
|---|---|
| Bank capacity | 200 Ah |
| Bank energy | 5,120 Wh |
| Bank energy | 5.12 kWh |
| Batteries needed | 4 |
- Only combine batteries of the same model, age and state of charge. Charge each one fully on its own before connecting them.
About this calculator
Wiring batteries in series (positive to negative) adds their voltages and leaves the amp-hours the same. Wiring them in parallel (positive to positive) adds their amp-hours and leaves the voltage the same. Either way, total energy in Wh is simply the sum of every battery, but the voltage you end up with decides which inverter, charge controller and cable sizes you need.
Enter one battery's specs and how you plan to wire the bank to see the resulting system voltage, capacity and energy.
How to use it
- Enter the voltage and Ah of a single battery.
- Enter how many batteries are in series in each string. This sets the system voltage.
- Enter how many of those strings are connected in parallel. This sets the capacity.
- Use the bank voltage and Ah in the runtime, inverter and wire-size calculators.
The formula
Bank voltage = battery V × batteries in series.
Bank Ah = battery Ah × parallel strings.
Bank Wh = bank voltage × bank Ah = battery Wh × total batteries.
Worked example (default values)
Inputs
| Voltage of one battery | 12.8 V |
|---|---|
| Capacity of one battery | 100 Ah |
| Batteries in series per string | 2 |
| Parallel strings | 2 |
Results
| Bank voltage | 25.6 V |
|---|---|
| Bank capacity | 200 Ah |
| Bank energy | 5,120 Wh |
| Bank energy | 5.12 kWh |
| Batteries needed | 4 |
Tips and common mistakes
Why go to 24 V or 48 V? At the same power, doubling the voltage halves the current. Half the current means a quarter of the resistive loss, thinner and cheaper cable, smaller fuses and a cheaper charge controller. As a rule of thumb, systems above about 1,500-2,000 W of inverter output work better at 24 V or 48 V than at 12 V.
Fuse each string. In parallel banks, a fault in one battery can draw current from all the others. A fuse on each string's positive lead limits that.
Frequently asked questions
Is series or parallel better?
Neither is better in general. Choose series to reach the voltage your inverter or controller needs, and parallel to add capacity at that voltage. Most larger systems use both.
What do two 12V 100Ah batteries make?
In series, 24 V 100 Ah. In parallel, 12 V 200 Ah. Both store about 2.56 kWh with LiFePO4.
Can I mix old and new batteries?
It isn't recommended. The weaker battery limits the bank and gets stressed. In series it can be over-discharged, and in parallel it drags down the others.
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Estimates for planning only, based on the assumptions shown. Real-world performance varies with equipment, temperature and installation. Updated October 19, 2026. See our methodology.