Series and Parallel Battery Calculator
Plan a battery bank and see how series and parallel connections change voltage, capacity, energy and the wiring diagram.
How series and parallel battery connections change a bank
Batteries connected in series add voltage while amp-hour capacity stays the same. Batteries or equal series strings connected in parallel keep the same voltage and add amp-hour capacity. The total stored energy is the voltage and amp-hours of one battery multiplied by the number of batteries, so rearranging the same matched batteries changes bank voltage and capacity but not total watt-hours. The diagram shows connection topology, not a complete installation design. Cable size, fuses, disconnects, BMS limits, balancing and permitted series or parallel counts must come from the equipment manufacturers and a qualified installer.
Battery count = series count (S) × parallel count (P)
Bank voltage = one battery voltage × S
Bank capacity (Ah) = one battery capacity × P
Bank energy (Wh) = one battery voltage × one battery Ah × S × P
Theoretical bank current = current per string × P
Worked examples
Four 12 V 100 Ah batteries as 4S1P: 48 V, 100 Ah and 4800 Wh.
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Four 12 V 100 Ah batteries as 1S4P: 12 V, 400 Ah and 4800 Wh.
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Six 12 V 100 Ah batteries as 2S3P: 24 V, 300 Ah and 7200 Wh. If one string is rated for 50 A, the arithmetic total is 150 A, but the real limit may be lower.
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Frequently asked questions
What does 2S3P mean?
Two batteries in each series string and three equal strings in parallel: six batteries in total.
Does series connection increase amp-hours?
No. It increases voltage; Ah remains equal to one battery when there is one series string.
Does parallel connection increase voltage?
No. It increases Ah and potential current while voltage remains equal to one battery or one series string.
Why is total watt-hour energy unchanged when I rearrange the same batteries?
A higher voltage is paired with fewer parallel amp-hours, or vice versa. V × Ah remains equal to the sum of the individual battery energies.
Can I mix different batteries?
Do not assume that batteries of different voltage, chemistry, capacity, age or state of charge can be combined safely. Follow the battery and BMS manufacturer's permitted configurations.
Is the calculated current a safe fuse or cable rating?
No. It is only an arithmetic total. Real limits depend on the cells, BMS, terminals, conductors, fuses and connections.
Why can the diagram be omitted for a very large bank?
The numerical result still works, but diagrams above the rendering limit become unreadable and are intentionally skipped.
Is the SVG a wiring plan?
No. It explains polarity and topology only. It does not specify protection, conductor size, isolation, balancing or compliance requirements.
Sources
- Victron Energy, Wiring Unlimited — battery bank wiring: https://www.victronenergy.com/media/pg/The_Wiring_Unlimited_book/en/battery-bank-wiring.html