I happened to be given 7 laptops that were destined for the landfill. All of them came without DC power adapters. Realising it would take a long time to receive DC power adapters by mail, I looked around.
Looking through my excessive 5v - 12v power adapters I found DC jacks that fit each of the laptops and cut each of them off.
The laptops I wanted to charge all required 19v inputs.
I placed 5 18650 cells in series, soldered wires them to the DC jacks, added a diode to the positive end and checked with a multimeter to get a voltage around 19.5v (inner being positive and outer shield ground.)
However, once I plugged the batteries into the DC jacks of each of the laptops, nothing happened. Except for one laptop which consumed ~10mAh from the five 18650 cells, but that was it.
Is there more to a DC power adapter? Why do (good quality) 18650 cells not work for the job?