Courtesy of Neil C here is the answer to a previous blog question regarding the "white box" in the lineside cabinet. Inside there are two 2v 25AH cells, a float charging circuit and the track feed resistor.
Having seen a picture of the rails on one of the other blogs there appears to be a good coating of rust - I suspect a bit of running will be required to get the circuits working effectively.
These are the cells:
Hope you enjoyed this exciting blog!