alt Hacker NewsBased on the work the person has done, if they wanted to make something with an exceedingly long battery life, and the battery setup there already seems to be basically a 1S li ion, they could graft in a back side battery holder for two high quality 18650 cells in parallel. It would probably last weeks.
A 10000mAh pouch battery would take up less room and provide more battery life. They are almost as cheap as 18650s too.