If you have an old laptop battery pack laying around you might be interested to know that you can re-purpose the cells instead of throwing them away. The laptop battery needs to be composed of 18650 type Li-ion cells otherwise this trick will not work. How to find out if your laptop battery is made out of these cells? Just cut the pack open carefully.
Where to start
First we need a some housing to hold the batteries and the charger. Luckily for us you can buy DIY powerbank kits on Ebay, Banggood or any other Chinese website. Keywords are 'powerbank' and 'DIY' or 'kit'. They should not cost you more than 3 of 4 dollars depending on how advanced the model you choose is.
Build it together
I got a kit for a four cell powerbank and as the backside optimistically notes it is supposed to deliver 12000mAh or 41Wh which is completely rubbish as I am about to put four used 2200mAh cells in it. Theoretically I am able to get 8800mAh out of it, but I am not sure these used cells will manage that.
The kit is delivered in a plastic bag and consists of these bits:
My kit has a display that show the amount of charge left and which USB is active. Also it has an emergency flashlight.
Using a dremel and a hacksaw I dismantle the old Fujitsu-Siemens laptop battery pack. It is made of six 18650 type cells. Be careful to not to cut too deep or you will damage the cells or the battery monitoring electronics that is inside the pack. For our purpose we only need the cells. You can discard the plastic housing of the pack and the monitoring electronics included: (Yay, genuine Samsung cells)
As shown in the image above my cells were already connected in pairs of two. Since I need four cells in my pack I need to connect two sets of two in parallel to the charge controller of the powerbank. Use some wire and imagination to connect the four cells:
(It works, connecting a micro USB the display shows we are charging...)
Now build it all together:
As you can see it is a snug fit, but after some fiddling it all fits. It all seems to work great.
I have not done any serious performance tests with this pack but I can seemingly recharge my Cheerson CX-10A quadcopters endlessly. The future will tell how this pack will hold...