Making a battery pack out of 8 cells in 4S2P configuration
It would be better to wire 2 series' of 4 batteries parallel to each other, rather than series wiring 4 parallel pairs together.

This is because you should add shunt/balancing resistors to each battery (or series of batteries) to ensure that every parallel unit "does its share," rather than one battery/series with slightly lower internal resistance burning itself out by performing (sometimes as high as) 90% of the work.

To balance parallel power supplies like this, figure out your anticipated max. amperage load, then size a resistor to cause ~10% voltage drop at that load; then attach a resistor of that value to each lower supply. This will cause a total voltage drop of ~5% in the shunt resistors (so 95% efficiency remaining) at max. load, and less loss at any lower load.

Like this: