Power cells in the SW 'verse tend to make anything in the real-life 21st century very caveman-like. Maybe pre-caveman

From blasters to starship weaponry, it's best not to think about it

The efficiency , especially in a lightsaber , must be insane. Luke/Anakin's saber just as an example; it probably sat in Obi-Wan's trunk for nearly two decades before it was ignited again. And now, after being lost for god alone knows how long in Cloud City (and surviving that fall...) it ignited without a beat as was used in combat. More than once. The whole bit with Ren's using a "broken crystal" is just stupid. For one thing, looking like a flawed piece of shit isn't kewl. Or intimidating. It looks like a flawed piece of shit. In fact, way back when we only had 3 movies to complain about

there was a bit in one of the EU books that didn't suck where Luke was assembling his new lightsaber using a book in Obi-Wan's house. He had a line where he paused activating it, since "here lies Luke Skywalker, hero of the Alliance, fried to a crisp, because he couldn't follow a simple circuit diagram.."

wasn't the thing he wanted on his headstone. So making these things precisely is one of the skills a jedi -and sith - have to master.