Of course they are also working on batteries for storing traction power too, but the recent (last month!) announcement of this was of an experimental unit (for GWR▸ ), and the agreement with Hyperdrive (last July) was to develop batteries. So it doesn't sound like they have one sitting on a shelf suitable for a production order.
At the time of the recent announcement, I tried to picture what type of battery would be needed to get a fully laden
IET▸ moving away from a platform without some sort of meltdown. My inner cynic, seldom far from the surface, thought the idea was a bit of a publicity stunt to stop people asking when the first electric train would arrive in Penzance. Presumably, the general idea is to use the batteries to keep moving once the diesels have helped the train to its top speed. I wonder if it is worth GWR's while, although I suppose it might cost nothing to let a private company develop something that they may or may not use.