Powerbank From 18650 (50Wh)

The end result of this project will be a compact powerbank (14Ah) powered by seven 18650 lithium cells.

What you need for the project

- a charging board for the lithium cells (I got mine out of an old powerbank)

- 7x 18650 lithium cells (I got mine out of an old e-bike battery)

- heat shrink in various sizes

- soldering iron + some solder

- wire cutters

(- helping hands, they help for soldering :))

First, I disassembled the e-bike battery pack while trying to save as many of the soldering tabs possible which are spot welded on the cells from the factory. This will make it easier to solder them together later.

Once I had seven single 18650 cells, I tried different arrangements of the cells in order to find the most efficient shape (with as less 'empty space' between the cells as possible). I settled on the hexagon with a seventh cell in the center as shown in the picture. Anything bigger would get huge or have an inconvenient shape.

I placed the cells on the table and wrapped around some tape to make them stay in place. Make sure the solder tabs are facing the right direction to solder them onto the next cell. I soldered them all in parallel, so all negative poles facing upwards and all positive poles facing downwards (or vise versa).

The math:
3.6V (stay the same)
2Ah/cell * 7cells = 14Ah
3.6V x 14Ah = 50.4Wh for reference: a typical phone battery has 12Wh / a laptop around 50Wh of capacity

After soldering the cells, it's now time to add the charging board:
One wire from the positive side of the battery to the + Pad on the charging board.
One wire from the negative side of the battery to the - Pad on the charging board.

Test it to see if it works and the on to the next step!

In order to make an enclosing for the batteries I wanted to heatshrink the whole pack into a large heat shrink (as seen in the next step). But first, the exposed solder pads of the cells needed to be covered to prevent from shorting the cells. I cut two transparent plastics in the shape of circles and put the on the top and bottom of the battery pack. In order to prevent it from slipping while I'm working on it, I drilled two little holes in each plastic piece and secured them with some strong wire (tied it down as much as I could).

The Last step was the heat shrink. I cut it about 5 cm longer than the cells are tall to have some excess at the bottom and top of the pack. I used the excess to bend it down on the round plastics as long as the heat shrink is hot and flexible (as neatly as I could) to make a tight fit (as you can see in the pictures).

Last but not least, the cutouts for the two usb-a ports and the micro-usb port. This worked better than expected using a sharp cutter.

Now charge it up and you are done.

Congratulation to your own powerbank!

Enjoy!