This work analyzes galvanostatic charging of a single-phase storage particle where the insertion kinetics are limited by solid-state diffusion combined with an ohmic resistance at the particle surface, in a coating (or SEI), or in the electrolyte. Using the Nernst-Planck formalism, the “optimal” dimensions in six particle geometries are derived as a function of the material transport properties. Special attention is given to geometries in which ions and electrons are transported over different length scales (“wiring lengths”). The results yield quantitative guidelines for the optimal particle size and carbon spacing in a battery insertion electrode. A strategy for increasing electrode thickness based on a particle size gradient is also discussed.