RePower

Recently I became an owner of 5 (five) "ancient" tablet PCs (HP Slate 2) and found them verrry interesting from inside ... hmmmm... side. Among other components LiIon batteries were found, 2 pcs in every tablet, upto 15Wh per cell. Measurements found out the perfect capacities, almost 4300mAh per cell (while they are marked as 4000mAh). Thank you, HP, for your careful choice of components suppliers years ago! As I have already owned some PowerBank PCB modules that were not found to be of any use for the project they were bought for, the clear thought came to me :) So here is it, the 8000+ mAh power bank with dual USB output and as blue as every chinese device do backlighted LCD display (not very informative but why not have one).
You need:
1) 2x LiIon cells from HP Slate 2 tablet PC (hard to unstick due to the same "careful choice of components suppliers" - I mean, glue suppliers too). Or the same size: 6.1 x 67 x 90 mm. Or smaller.
2) 1x Dual USB PCB like https://www.aliexpress.com