Lithium-ion nominal cell voltages
The nominal voltage of lithium-ion is normally 3.60V per cell. Some cell manufacturers mark their Li-ion as 3.70V/cell or higher.
How is a cell's nominal cell voltage defined?
The nominal cell voltage is the average voltage a cell outputs when charged.
Parallel chains which tend to be self balancing since the parallel connection holds all the cells at the same voltage. Being in parallel allows charge to move between cells freely.
Therefore it is only necessary to balance groups of cells that are in series.