How can you wire 4-12 VDC batteries together to get 24 out of them?

You cannot wire 4-12 VDC batteries together to get 24 VDC. The maximum voltage you can get from wiring batteries in series is the voltage of the individual battery multiplied by the number of batteries. For example, if you wire 4-12 VDC batteries in series, you will get 48 VDC.