"Inside the insulated cask of the battery, the electromotive apparatus cracks the energy out of oil and converts it to electrical charge."
Combustion cells are a type of liquid-fueled energy cell which produce power from Oil. Combustion cells are inefficient power sources, weighing three times as much as normal cells when full but only holding 60% as many charges.
As an unidentified Artifact, it may appear as "small trinket" or "small cube", occasionally containing a few drams of oil.
Each dram of oil can produce 750 units of charge, and it can hold a maximum of 8 drams. A fully fueled cell can provide 6000 units of charge.