I now have the answer.
The dimensions and spec are as follows.
Shimano BT-E8020 36V = 14ah 504wh
Length 375mm
Width 86mm
Depth 92mm
Weight 2,915g
For comparison with my current Bosch external battery.
Bosch 36V 13.4ah 500wh
Length 319mm
Width 91mm
Depth 88mm
Weight 2,410g
The weight against manufacturers spec could obviously be inaccurate due to my digital scale, but there is still a difference of 505g between the two when using my scale.
A square was used for reasons of accuracy, and two squares used for when measuring the length.