Locking gas cap

assuming the call is not metal(?) and youve not watched 3hrs of youtube lock picking vids..lol

you can normally slowly drill just the center key hole slot out, via a series of small holes without going all the way thru the cap or generating too much heat. inners are mostly brass/aluminum, sometimes copper or stainless, depending on quality of cap.
Eitherway, this will remove some or all of the key tumblers, allowing you to then crank/pick via flathead screwdriver (or similar) the inners around and unlock it.
If the cell still has fuel in it and hasnt aired out for a good while, Id be extra careful or drain it via the fuel line and possibly back fill with water (aka: ubber safe method, similar to how they weld on steel fuel tanks). any tiny traces of fuel left inside THEN wouldnt be too spontanious, but built up vapors (if any) certainly are not a good mix with a hot drill bit/drilled metal and in a cell can take a long time to actually disapate on their own, unless evacuated.