[ianburrell]

Another idea to provide backup power is to have backup battery in the "key". The key wouldn't be need to be mechanical, but electronic, and could provide the juice for emergencies. Another option would be a "key" that acts as microUSB adapter to provide power from phone.

[pjc50]

Providing power through the key makes it an attack surface (what if I supply 5kV? can I use it for power-analysis attacks? etc)

[emhart]

Latter idea is mentioned in the post, though...clocking in at ~7500 words I blame absolutely no one for not getting to the end haha