Q:

What effect does replacing the load on a switch-mode power supply with a battery have on design?

I am working through a theoretical design for a solar charge controller for a battery bank where the battery voltage is strictly greater than the open circuit voltage of the solar array.
Most of the explanations of switch-mode power (a boost converter in this case) treat the load as a simple resistive load. I'm trying to understand what happens when the load produces its own voltage potential. Are there modifications needed to prevent the battery from feeding back into the inductor or discharging when not being charged?

A:

Here's a really rough conceptual model of your system (in a real switcher SW1 would be a FET).  The important thing to note is that if D1 is really a diode, then it simply won't conduct backwards.
To gain efficiency, modern switching converters use FETs for both the switch and the diode, in which case the thing could back-conduct from the battery to the solar cell -- but you could take care of that in your control circuitry.

simulate this circuit – Schematic created using CircuitLab

