The detail that jumped out at me first: each little cell pushes only 0.14 to 0.23 milliamps, yet wired together they manage to top up an 18650. AlansInventions pulled twelve cells out of cheap landscape stake lights and turned them into a working charger, all held in a purple printed frame arranged as a three-by-four grid.
The build started with tearing down the stake lights and freeing the cells. A single cell read about 2 volts on a Klein MM400 multimeter before anything else happened. After sketching the series and parallel layout by hand, the maker printed the cell grid plus an angled base with raised lettering on an Ender-3, everything in purple PLA. The cells then went into the frame, were soldered with black and red wire, and got fixed down with hot glue. Power flows through a blue TP4056 protection board fitted with female header pins, salvaged contacts grip the 18650, and the panel wiring finishes in alligator clips.
The layout runs four parallel columns of three cells in series for roughly 6 volts nominal. The finished panel outputs 7.2 volts and 85 mA, and direct sun measured 7.46 volts at 84.9 mA. Indoors under a lamp it dropped to somewhere between 3.6 and 6.2 volts.
One trade-off is flagged too: an on-screen note points out that PLA does not cope well outside. The narration also stacks this panel up against commercial ones and admits the project doubles as a lesson in how inefficient these tiny cells are, and the maker admits to wanting to quit partway through.
Project by AlansInventions. Watch it on their YouTube channel: