£9 may be a ripoff compared to the Turnigy packs, but space is so tight inside Spin Cycle that any other pack that has different dimensions just won't fit. The £9 packs are Hyperion ones; I had one already from four years ago that lived in Flatulence, but transferred it across to Spin Cycle when I was first wiring it all up. I then ordered more of the same pack for the size reasons mentioned, but also to keep consistency battery-wise between the beetles. Means I don't need to have different batteries for different beetles or need to fanny about with my battery charger settings at an event.