technical (noob) question: how long does trezor remember its keys if not powered up for years? at least a theoretical forecast/speculation, please. the concern is to move a part of funds to a trezor that would not be used frequently (at all in near future) and if there is something like an internal battery that should be taken into account for long period of inactivity?
The seed is stored in flash memory. It does not need power and the device does not have any internal batery. The minimal data retention of flash is usualy specified as 15 years, but this is the minimum that is guaranteed for devices stored in extreme conditions (85°C). When storing in normal temperatures, it should last at least 100 years according to this study:
http://www.freescale.com/files/microcontrollers/doc/eng_bulletin/EB618.pdf