Building a Huge 18650 Battery Powerbank DIY
EDIT: worked figures.

If you've settled on 16 cells, let's work some numbers.


Using a realistic figure for an 18650 cell (3400mAh) we get 219Wh for a 16-cell pack.
which works out to 43.8 Ah @ 5V for the pack
Weight for the batteries alone: 720g (45g/cell)


16 cells is double the size of a large laptop battery. At 5V @ 2A this battery will take about 20-30 hours to charge. That's a long time. Yes, you could do it, but why? Consider USB type C power delivery at least. That said, a 12V or higher charge input is more typical for a big pack like this.

Now, should you make your own pack? If you wanted to make more than one, and were willing to put the work in to fully productize it, sure. Do consider a balancing solution for your pack. Example (link).

Also have a look here for some DIY Li-ion battery solutions. Seems like what you're after.

Realistically though, for a one-off I urge you to consider another solution: use a pre-made Li-ion motorcycle battery with built-in protection and a warranty.

This outfit makes some good ones. Their 16-cell battery weighs 1.4Kg, so yes it's double the weight of the bare cells. But it's a fully-engineered, robust and warranted solution.

Another consideration: Li-ion batteries are banned for air travel. Check the current FAA regulations.