Light sabers follow a similar overall principle of ‘plasma bolt contained by some kind of coherence field’… but they use totally different internals to generate both the plasma and coherence field, and can seemingly just… do this nearly infinitely, never needing to ‘reload’, never running out of energy.

In the comics taking place tens of thousands of years before the movies the Jedi have to carry large energy cells with them. They are attached with long cables to the hilts.