The Next Generation (Nextgen) Energy Storage program, based in the Australian Capital Territory (ACT), Australia, is one of the largest roll-outs of household batteries world-wide. Beginning in 2016, it will eventually involve up to 5000 households and businesses. Energy data collected as part of this trial will provide an unprecedented opportunity to understand both the economics of battery storage as well as the technical impact of household batteries on the grid.In this paper, we provide a description and an overview of this publicly-available data set. We outline our data cleaning process and provide some first insights into how batteries are impacting customer power consumption. In particular, we show how solar generation with battery storage reduces evening peak load, and substantially reduces grid exports. Mean solar self-consumption in 2018 without batteries was 33.7%, compared to almost twice that (57.3%) with batteries. Finally, we provide suggestions for further research using the data set. An open-access version of these data will be made available by the ACT government in July 2019.