This document discusses energy storage technologies and their potential role in mitigating climate change. It outlines an approach to assessing promising technologies which includes literature review, expert elicitation, technology selection, energy system modeling. It finds that cost is a major factor and that lead-acid, redox flow and lithium-ion batteries show promise. By 2020, improvements will likely come from manufacturing advances rather than new chemistries, but longer-term R&D could enable new technologies by 2030 if given sufficient funding and support. Energy storage could significantly aid renewable energy deployment but both R&D investment and policies to support deployment will be needed to realize its potential benefits.