A parallel connection is when multiple batteries (up to 4 max) are connected in order to provide increased capacity. See Leisure Battery User Manual for instructions on how to properly connect batteries. A series connection is when multiple batteries of the same type and voltage (up to 4 max) are connected in order to increase voltage required, i.e., 24V, 36V, 48V. See Leisure Battery User Manual for instructions on how to properly connect batteries.