Lithium dendrites may cause internal short-circuiting, fires, and even explosions. Unfortunately, the study of dendrites has been hindered by the impossibility of in situ observations. This work proposes a new double-scale in situ experimental setup that records the dendrite evolution of half and full cells during small-current-density electrochemical testing. The experiments confirmed that dendritic growth eventually connects the cathode to the anode, with significant effects on the cell voltage. In the full and half-cells, the attached dendrites decreased and increased the voltage, respectively. During discharge, the bubbles generated by the side reaction affected the dendrite evolution in both cells. A detailed model of lithium dendrite evolution mechanism in the anode is also proposed. (C) The Author(s) 2019. Published by ECS.