I emailed Brett over at conics.net, and he said that the new EA-BL11 battery that comes will the SL-C3000 will be compatible with the Cxx0! If you have a C700 or C750, I'm sure you will need the battery cover that comes with the EA-BL08K in order to use this battery, but C760 and C860 owners should be able to use it right away.
I emailed him back to find out when they will be available, what the performance increases are, and how much it will cost. Hopefully he'll write back soon.