-Each Original has a stockpile of refined energon - both for their own use, and to give out to the Refugees. Each handles it in their own way; most have a dispensary of some sort where anyone can come up and take a cube. (Or ten.) If you're away from the Haven, there's raw energon to be harvested, and if you know how to refine it there's nothing stopping you.
All things that are able to imbibe Energon will find at least /something/ they can process - and if it's completely unpalatable, Nexus Prime could probably fix that for you. If you're on his good side.

-We really, really wouldn't advise finding out. The Firstforged can get a little...possessive...about something so directly 'theirs', and wouldn't take kindly to someone even damaging an Acolyte.

-With enough expertise, someone could hypothetically hack the lock - or reinforce it /against/ hacking.