Originally I'd thought no further than using the under floor detail parts from the Ratio Kit. However a visit to Dart Models for some detailing parts which I did need, pipes, ventilators, lamps etc. set me off in another direction altogether.
#15 is documented as having a dynamo and it can be clearly seen on the left side to the left of the middle door. However no battery box is visible from either side so I haven't bothered to add one!
The Dart dynamo is a neat 3 part white-metal kit easily assembled and shown here along with the added V hangers and brake control rods. While I've no details of the setting of this, the helpful 3D graphics of the new Genesis coaching stock provided me with a very good idea of how it could well have been configured.
Edited by BWsTrains