Battery Series Parallel Configuration Calculator
A battery pack is built by wiring identical cells in series and parallel. Series strings add voltage; parallel strings add capacity. This calculator takes a single cell's voltage and capacity, plus the number of cells in series and in parallel, and returns the pack voltage, the pack capacity, the total energy in watt-hours, and the total cell count. It is the standard tool for designing the S by P configuration of a lithium, NiMH, or lead-acid pack to hit a target voltage and runtime. Use matched cells and a balancing battery management system in practice.
Series-parallel pack formula
pack voltage = cell voltage * S
pack capacity = cell capacity * P
pack energy (Wh) = pack voltage * pack capacity
total cells = S * P
S is the number of cells in series and P the number of parallel strings. Series multiplies voltage; parallel multiplies capacity. Energy is the product of the resulting pack voltage and capacity.
Pack design notes
- Series raises voltage to match a load or charger; capacity stays at one cell.
- Parallel raises capacity and current capability; voltage stays at one cell.
- Use cells of the same chemistry, capacity, age, and state of charge.
- Series lithium packs need a balancing battery management system.
- Total energy equals single-cell energy times the total number of cells.
Series parallel packs: frequently asked questions
How do series and parallel cells affect a battery pack?
Cells in series add their voltages while keeping the same capacity; cells in parallel add their capacities while keeping the same voltage. A pack described as S series by P parallel has voltage = cell voltage * S, capacity = cell capacity * P, and total cells = S * P.
What is total pack energy?
Pack energy in watt-hours is the pack voltage times the pack capacity in amp-hours: energy = (cell voltage * S) * (cell capacity * P). It equals the single-cell energy times the total number of cells, since each cell contributes its own watt-hours.
Why connect cells in series?
Series connection raises the voltage to match a load or charger that needs more than one cell can provide. For example, four 3.7 V lithium cells in series give about 14.8 V. Capacity stays the same as one cell, but voltage multiplies by the series count.
Why connect cells in parallel?
Parallel connection increases capacity and the available current at the same voltage. Two 3,000 mAh cells in parallel act like one 6,000 mAh cell at the same voltage, extending runtime and supporting higher load currents.
Should cells in a pack be matched?
Yes. Cells should be the same chemistry, capacity, and ideally the same age and state of charge, so they share load and charge evenly. Mismatched cells can overheat or fail. Always use a balancing battery management system for series lithium packs.
Official sources
- NIST: SI units (volt, ampere, watt-hour).
- U.S. Department of Energy: Batteries and energy storage.
Reviewed by the CalculatorHub team, edited by James Graham, 16 June 2026. See our methodology.