Adding 18650's to anexisting powerbank.

I have a Blackweb 18,××× mah powerbank and a crap ton of 18650’s. My question is how would YOU go about doing this? I have the knowledge and skills to do this myself now, but I often overlook small details causing big issues… So if anyones done this or has any ideas on how to make this project happen reliably and relatively safe I’d love to hear your thoughts.

Had a quick google and couldn’t find the product you’re refering to… but short answer to “How would I go about doing this…reliably and relatively safely

…I wouldn’t.

You don’t specify what state the ‘crap ton’ of 18650’s are in - are they new, the same brand/capacity/age/usage cycles? Are they a bunch of random ones you’ve pulled from old laptop batteries?

There are loads of lithium ion testing guides online from the DIY powerwall people, if you’re serious about using the cells, maybe have a look at those?

Easiest solution to requiring larger power bank capacity: buy a larger powerbank.

If you’re dead set on using these things, read up on some of the hazards of mixing cells in series, adequately test the cells you want to use and then build a powerbank from scratch using a DIY board found on ali/ebay/etc.

The batterys I had in mind all came from a single source and were all tested before and after their initial charge, they were used in a powerbank that I had built with an ebay diy powerbank charging board so in theory they are still relitivly similar in voltage.
My initial idea was to try and expand the capacity of the powerbank and build apon it to make a solar generator of sorts, like the cheapy harbor freight/Amazon ones. Thank you for the reply and especially the words of caution, too often people will give bad advice just to sit back and watch the carnage.