Who said old button cell batteries are useless?
Stack a lot of them in series and squeeze every last milli-ampere from them...or create a high voltage DC source.
Just stack all your (20mm) button cells +/-/+/-/etc. in series.
I filled mine half-full and measured 63V !!!
0.4mm Nozzle, 0.2mm Layer Height
www.123-3d.nl PLA 1.75mm
20% HoneyComb, and 5 layers wall, top and bottom.
Use a 5mm Brim and 5mm Skirt.