Implementing alkali metal anodes and replacing flammable liquid electrolytes with solids promises to deliver higher energy densities and greater safety than conventional Li-ion batteries. However, challenges at the interfaces must be addressed to realise this potential. Alkali metal dendrite growth, even at modest rates and even when paired with dense, well-sintered solid electrolytes, leads to short circuits and cell failure. We have investigated the effect of cycling conditions on the formation of voids and dendrites under controlled applied pressure. The results reveal the significance of plating/stripping current densities and pressure on cell failure. We propose a model for void accumulation and its effect on dendrite formation. These results and their implications for the operation of a failure free all-solid-state battery will be discussed.