Told my wife we had spare battery packs for camping, so I built one the night before we left

Did almost the same thing last summer before a fishing trip with my brother. Told him I had a spare charger sorted, then remembered the one I acutally owned had swollen up and gone in the bin months earlier. Ended up pulling a couple of 18650s out of an old laptop pack I'd been hoarding, wired them parallel to a cheap board off AliExpress, and stuffed it all in an Altoids tin with foam wedges so nothing shifted around in there. The tin thing is worth trying if your next build still looks rough. Nobody suspects a mint tin, and the metal stops it feeling lumpy like yours did. My brother commented that it was nicer than the one he paid thirty bucks for, wich felt criminal.

One thing I learned the hard way though: check that the cells you're pulling are actually charged before you promise anything. Mine sat at maybe half capacity beacuse the laptop had died years back, so it topped up his phone once and then gave up halfway trough the second charge. Had to fess up on the drive home anyway. Now I keep one finished bank in the glovebox and a spare module with a cell in a drawer, purely so the next improvised promise doesn't require a midnight soldering session again.

I did the panic build once and swore never again. Ours was a school trip morning and I'd promised my daughter a charger for the bus, so at 11pm I was hot gluing a charging board into an old soap container with a 2600mAh cell and praying the glue didn't shift anything. It worked but the port ripped loose on day two becasue there was nothing anchoring the solder joints except the glue itself. After that I started keeping two finished ones in the camping bin as spares. Same cheap boards, but now the cells sit in proper plastic holders, the wires are short and strain relieved with a dab of hot glue on each joint, and everthing lives in a project box with the USB cutout filed smooth. Takes maybe twenty minutes to build one properly on a quiet evening versus an hour of swearing at midnight. Honestly the spares have paid for themselves several times over. The trick I've found is treating them like torches or spare batteries, just another thing that lives in the bin year round. Then when someone asks 'do we have a charger', the answer is actualy yes and you can even hand over one that doesn't feel like a wrapped burrito. My wife still teases me about the soap container though, so I guess we all have our version of the warm lumpy story.

The 'felt warm and lumpy' answer is where these things unravel. Mine came apart when my other half plugged the homemade one into her tablet and it charged at half the usual speed, so the cover story needs to cover performance too, not just looks. I've been wiring control panels for 22 years and even my builds look suspect without a proper enclosure, so now I keep a batch of blank adhesive labels in the toolbox and slap one on any project that might get inspected. A fake brand name and a spec line on the side works better than tape ever did. Just don't print a capacity number you can't back up.

Update: the proper case turned up and it acutally looks like a real product now, so the lumpy problem is solved. But the reply about performance being what gives these away was right on the money, becasue she used it again and asked why her phone charges slower on it than the wall plug. It's a single cell with one output so I don't think it can be fixed. Is that just what you get from a basic board, or is there somethig worth swapping?