Concentration of sulfuric acid
Simple and no waiting. Simply put flooded electrolyte gone, then drained and ready for the new one. You can make some for future use.
ATTENTION ! The acid output, is even more dangerous than the original electrolyte. Therefore, let me remind about the safety precautions - gloves, goggles (better mask-plate), special clothes, soda solution nearby, etc.
As the concentrated sulfuric acid is the precursor, i.e. It prohibited its manufacture, storage and use, in addition to legal persons having the appropriate permits.
These videos using acids described only as an experiment.