Control current to one of two loads on PCB
You could possibly get away with using a high power, super low Rdson MOSFET as a low-side switch (N-FETs have generally lower Rdson than P-FETs) for each device. If you get a MOSFET that has an RDSon of 4mOhm you'd have 1.6W dissipation on the FET at 20A. You could use the battery voltage to drive the MOSFET gates with either a gate driver IC, level translator, or inverting MOSFET (Something like a 2n7002 in common source configuration) to change the 3.3V control signal to a suitable gate drive level for that high of a current. Something like the Infineon BSZ009NE2LS5ATMA1 (1mOhm Rdson at 4.5V Vgs).