Pack design
Series and parallel configuration
How cells are connected to reach the required voltage (series, written S) and capacity or current capability (parallel, written P).
What it changes in practice
A 4S2P pack has four groups in series with two cells in each group: nominal voltage is four times the cell voltage, capacity is twice the cell capacity, and current capability is roughly doubled. Series strings need balancing; parallel groups need cells matched in capacity, impedance and state of charge. The configuration is usually settled by the load voltage and the required runtime, and it determines the BMS channel count.
Why it matters when you specify a cell
Series count sets the voltage window and therefore the protection thresholds; parallel count sets the current each cell sees and therefore the grade you need. Decide both before comparing cells, because the same cell is a comfortable choice at 5 A per cell and an unacceptable one at 25 A.
Related terms
Read further
More in Pack design
Other terms in this group
From single cell to assembled pack.
BMS (battery management system)
The electronics that monitor cell voltages, current and temperature and disconnect the pack when any of them leave the manufacturer window.
Read the entry →Cell balancing
Equalising the state of charge of cells connected in series, either by dissipating excess charge from the highest cells or by moving charge between them.
Read the entry →Interconnect welding
Joining cells to busbars by resistance welding or laser welding rather than soldering, which is the accepted method for cylindrical cell assembly.
Read the entry →