26TH JULY
Battery
With the battery holder soldered in it was time to find a suitable battery.
I could not find any specific reference to a particular type of battery in the manual so I needed to consult the schematic diagram and the battery holder data sheet.
The schematic indicates that a rechargeable lithium ion battery is required.
The data sheet say that the 3008 holder is for a CR2450.
http://www.farnell.com/cad/2017758.pdf?_ga=1.241836161.260727887.1483275355
The battery voltage will be less than the output voltage of the charger.
With these considerations in mind I guessed that the batter is a LIR/PD2450.
(LIR = Lithium Ion Rechargeable)
I downloaded a data sheet for a PD2450 to confirm that it is 3.7 volts.
[30/02011] - 
As an experiment, I purchased a CR2450 non-rechargeable battery to see if it would work with the XL_Star board.
It is only rated at 3 volts but measured 3.2 volts out of the packet.
Before attempting this, I ensured that the unit was disconnected from everything to ensure that the battery charger would not risk exploding the battery.
The battery fitted in like a bought one. (Funny that, it was!) 
Flicked on the power switch and hey presto, the program ran! 
I switched it off and I removed the battery for safety.
For how long this battery would run is another matter. Maybe this can be found out at a later date.