Custom NBT from block to item

Im trying to make a battery item that drains energy from a block
 

for some reason its not working as intended, the energy is drained from the block infinitely but theres no power added to the item, its stuck at 0.

Also before anyone asks, no im not using FE, i want my mod to have its own energy system using NBT and so far it worked great, only now that im trying to put energy from a block into an item it wont work for some reason.