[Clutchbob]

The diagram is very misleading. If the black lines represent connections, they would be putting shorts across the cells!!
Many multicell packs include a balance plug. these simply bring out the interconnections between the individual cells. A three cell pack would then have four wires, the outside wires usually being the overall voltage in series and adjacent wires the voltage of the individual cells. A few of the new Lipo chargers can make use of this plug to balance each cell during charging. Manufacturers also make balancing adapters.
Balanced cells are critical in Lipo packs. Repeated use can unbalance cells and can allow for overcharging or overdischarging of an individual cell.
I recommend that if you are building your own batteries that you provide a way to balance in this way. It's very easy to then charge each cell individually, if you don't have a balancer, fully charge each cell with a single cell Lipo charger one at a time every so often. You should do this with a newly built pack before you charge in series the first time as well.
A voltage check will confirm which wires are the individual cells when you're not sure of the plug configuration of a prebuilt pack.
Be carefull building packs, NEVER short cells.