batbox power grid issue

[CreeperGoBoom]

Ive come across something rather interesting that i need verifying

OK here's what i've done

i've got a main power grid type thing happening, basically a heap of wires going to an LV transformer, to 2 batboxes daisy chained

here's what i found, while the chain is: LV transformer> batbox1> batbox2> grid

while batbox2 is connected to the grid via glass fibre cable batbox 1 is outputting power fine through batbox2 however batbox2 isnt charging

if i swap the glass fibre cable with an insulated copper cable which outputs from batbox2, batbox2 starts charging, nothing is using the power by the way

anyone know why this is happening?

edit: panel is a 13eu/t