The battery components are connected in series and in parallel. The battery packs in parallel require the same voltage of each battery. The output voltage is equal to the voltage of one battery. The parallel battery pack can provide a stronger current. There is no excessive requirement for the series battery pack.
Just ensure that the battery capacity is about the same. The series battery pack can provide a higher voltage.
Battery packs are used extensively in our lives. TV remotes, electronic toys, and flashlights have battery packs in series.