A DIY USB power bank made from an old laptop battery from DoItYourselfGadgets:
A situation many can relate to: an empty smartphone battery and no outlet around! That’s exactly why I recycled an old laptop battery into an USB power bank.
This article will show you the basic powerbank circuit consisting of Lithium cell charging circuit, boost converter and toggle switch as well as my improved version with self activating boost converter and LED status indicator and homemade housing.
It all started with an old Lenovo laptop battery. I carefully pried it open to examine the cells. Three packs of two parallel 18650 Lithium 2200 mAh cells were connected in series.
According to some internet research about these cells, one should be able to use all three of these packs in parallel, as long as all the individual packs of two have intact cells.Simply measuring their voltage, carefully charging them under controlled conditions and checking if they hold their charge for quite some time determined all cells were still fine.….
Read more Here