The resulting material displays all the electrical properties associated with a capacitor, meaning that it can charge and discharge its full capacity almost instantly. But it has a storage density that’s right at the low-end of the range seen in lead-acid batteries. It’s also stable over multiple charge/discharge cycles and holds on to 90 percent of its capacity even after being charged for 300 hours straight.

via Simple technique puts graphene capacitors on par with lead-acid battery | Ars Technica.