In one embodiment, a solid state battery includes a first cell stack including a first solid-electrolyte separator positioned between a first cathode and a first anode, a first base layer including a first base portion positioned directly beneath the first anode, and including a first lateral extension extending laterally beyond the first anode, a second cell stack beneath the first base layer and including a second solid-electrolyte separator positioned between a second cathode and a second anode, a second base layer including a second base portion positioned directly beneath the second anode, and including a second lateral extension extending laterally beyond the second anode, wherein the second base portion extends laterally beyond the first lateral extension, and a multiplexor (i) in electrical communication with the first base portion through the first lateral extension, and (ii) in electrical communication with the second base portion through the second lateral extension.