gearup,
Adam was correct in his statement below. Each pair of cells (or paralleled cells) are in series with each other to create a 3s pack.
The balancer connects to each pair of cells that are in series with each other, and balances the three pairs to each other.
I am not sure what Roger is talking about. Unless he made his own packs by placing two 3-cell packs in parallel with each other, his story doesn't make sense. This is not the technique used by manufactured packs from vendors.
Let's use the pack below as an example. It is a ThunderPower 5S3P "Pro Lite" 6000 mAh high capacity, high voltage, Lithium Polymer pack pre-connected with Deans Ultra connector and pre-wired with a cell balance plug that mates with the 2-5 cell LiPoly cell balancer (TPB205).
Cell balancing will keep your valuable batteries in top working condition. Monitoring your battery with cell balancer while charging gives you the added safety of an over voltage alarm. Note that while ThunderPower uses two separate devices to obtain balanced charging, the FMA Direct chargers do it automatically in a single product.
While this pack does contain 15 cells, electrically speaking, it only has 5 "super cells" and therefore only taps to the 5 different voltages. Each "super cell" is made from three smaller single cells in parallel. When you weld identically matched Lithium cells together, they are treated as a single cell. The resultant "super cell" has the combined capacity and current delivering capability of the original cells added together.