Use this wire harness to put one 12v battery in a front compartment and one 12v battery in a rear compartment and get 24v in series.
To complete this wiring we recommend getting one female connector with a fuse holder and one without. (You only need one fuse in the circuit). These will attach to your batteries. Includes 52" of wire.

When combining batteries be sure they are the same brand, age, chemistry and amperage.

We also sell this as a complete package with batteries, linked below.