BatteryCalcs
BatteryCalcs — calculation report

Series and Parallel Battery Calculator

Plan a battery bank and see how series and parallel connections change voltage, capacity, energy and the wiring diagram.

V
Ah
S
P
A

Series raises VOLTAGE. Capacity in amp-hours stays the same.
Parallel raises CAPACITY in amp-hours and the allowed current. Voltage stays the same.

 

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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. Open this example in the calculator Four 12 V 100 Ah batteries as 1S4P: 12 V, 400 Ah and 4800 Wh. Open this example in the calculator 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. Open this example in the calculator

The Tesla Model S pack: 7104 cells

The Tesla Model S 85 kWh pack is sixteen modules, and each module is six cells in series and seventy-four in parallel. Together that is a 96S74P arrangement and 7104 cells of the 18650 size. Enter the catalogue figures for a single cell, 3.6 V and 3.4 Ah, and the calculator returns about 346 V, 252 Ah and 87 kWh. The car is badged 85 kWh, and measurements of real packs land near 81 kWh. The three numbers do not contradict each other: catalogue capacity is measured at a gentle discharge, the badge is a marketing name, and the car never uses the full voltage range anyway. Above one hundred cells we draw a simplified schematic, because seven thousand rectangles would explain nothing. Open this example in the calculator
Ready-made electric car pack

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