RE: So let's see if I've got this right.
Series and Parallel Cells:
As with NiCd or NiMH cells, Lithium batteries can be wired in series to increase voltage. Lithium cells can also be wired in parallel to increase capacity and current delivery. A combination of series and parallel Lithium cells can be used to create a more capable flight pack for powering larger motors or increasing flight duration. A common designation seen to describe the configuration of multiple cell Lithium packs is the XsYp label where X is the number of cells in (s)eries and Y is the number of cells in (p)arallel.
The voltage of a single Lithium cell is about equal to three NiCd cells. A Lithium cell measures about 4.2 volts unloaded when fully charged and about 3.6 volts when loaded. The cells should not be discharged under 3 volts although it is ok for them to go below this level for short durations which may typically happen at the end of a flight until the ESC’s Low-Voltage Cut-off (LVC) or disconnect circuitry turns off the motor. The capacity of a cell is often referred to as “C”. For example, a Kokam 145mAh Lithium cell has a 1C capacity of 145mAh.
The series/parallel diagram shows one pack of four Lithium cells in series and one pack of four Lithium cells in parallel. When the cells are placed in series, the voltage per cell is simply added. The four cell Lithium pack would measure 4*4.2v or 16.8 volts unloaded. Its pack designation would be 4s1p or simply 4s. When the cells are placed in parallel, the voltage remains the same but the capacity and current delivery are added. If the four cells are the Kokam 145mAh Lithium cells then the resulting pack would measure 4.2v unloaded and have a capacity of 145*4 = 580mAh (or 4C). The current delivery capability would also jump from about 700mA continuous current per cell to about 2800mA continuous current for the 4-cell combination. The short term peak current delivery for this particular cell is about double that so our 4-cell combination would deliver about 5600mA for 10-20 second bursts. Its pack designation would be 1s4p or just 4p.
The current delivery capability of Lithium cells is different for each type of cell and manufacturer. It is often a competitive debate among R/Cers and vendors. Like the cell capacity “C”, the current delivery capability is also refered to in “C”. For our example of the Kokam 145mAh Lithium cell, the continuous current capability is about 5C and the peak current capability is about 10C. This cell was actually among the first high performance cells on the market several years ago.