"One limitation of the technology is in the use of difficult-to-handle liquid electrolytes and the need for a dry and oxygen-free environment when making the new device."
Sounds like it will be a while.
"The researchers tested the device using nine bathroom tiles coated with the paint and connected to each other. When they were charged, the batteries powered a set of light-emitting diodes for six hours, providing a steady 2.4 volts..
If they were in series that means 0.27V each. 
"A set" might be 2. They might be running the 'set' at 5 mA. That would make the capacity of those 9 batteries 0.03 mAh (0.003 each).