Whilst rarely seen as an exciting technology, battery power is essential to most modern appliances and certainly those that can’t stay permanently plugged in (e.g. phones and cars). Driven by new commercial applications, significant gains are now being made in this area. Graphene, Aluminium Air and Solid State batteries for instance allow longer range and fewer charges. Another benefit of batteries is the ability to store cheap energy and use it at a time when that energy is more expensive. There are a number of examples of this in the home; for instance Tesla’s Powerwall, which charges from solar during the day and outputs at night. However, commercial application is not far behind; a recent example being the installation of a 5-tonne battery in Whitbread’s Premier Inn in Edinburgh (the first battery powered hotel in the UK). This allows the operator to sell energy back to the grid, eliciting an annual saving of £20,000 and reducing its carbon footprint. Battery storage works best when the main supply of energy is erratic (e.g. where there is significant reliance on renewables such as wind, which doesn’t always blow). However, as battery efficiency and solar power improves, so the days of reliance on a live feed of mains electricity might be numbered.