Quote Originally Posted by DE
If that was the case, then the ones inside 2nd Gen Dragon Slayers would run out after they used all the energy that was stored in the lacrima. And that certainly doesn't seem to be the case with Laxus. The Dragon Lacrima being the very life essence of a dragon explains why they don't ever seem to deplete.
You pump mana into the Dragon Lacrima like how your normal mana refills your container. When you decide to use it in a magical attack, the mana previously stored is now of Dragon attribute. That's what I mean by "they can expel Dragon magic".

If I go back to Laxus's Lightning lacrimas, I understood those to produce lightning magic, but you can charge them with any mana.