The structure of lead deposits (approximately 1mm thick) formed in conditions likely to be met at the negative electrode during the charge/discharge cycling of a soluble lead-acid flow battery is examined. The quality of the lead deposit could be improved by appropriate additives and the preferred additive was shown to be the hexadecyltrimethylammonium cation, C16H33(CH3)3N+, at a concentration of 5mM. In the presence of this additive, thick layers with acceptable uniformity could be formed over a range of current densities (20–80mAcm−2) and solution compositions. While electrolyte compositions with lead(II) concentrations in the range 0.1–1.5M and methanesulfonic acid concentrations in the range 0–2.4M have been investigated, the best quality deposits are formed at lower concentrations of both species. Surprisingly, the acid concentration was more important than the lead(II) concentration; hence a possible initial electrolyte composition is 1.2M Pb(II)+5mM C16H33(CH3)3N+ without added acid.