[stbtrax]

Electronics, if weatherproofed properly, will last a very long time. They don't have any wear and tear like mechanical parts so I'm not sure what would degrade other than the battery or misc connectors.

[brians]

Capacitor electrolytics.

Air bubbles in silicon, thermal expansion, and a zillion day night cycles.

Humidity and dust enter, contributing to occasional momentary shorts.

Oxidation anywhere you have electromechanical connections.

Magnetic stresses on any coil, any rectifier.

[kazinator]

Transistor aging: https://spectrum.ieee.org/semiconductors/processors/transist...

(Not likely to affect anything you'd mount on a bicycle, over any span of time relevant to a bicycle.)

[mkj]

Or shock causes a supercap lead to shear off, etc. I guess everything could be epoxy potted but then it isn't repairable.

[jacquesm]

Cables, servos, brushes, switches and so on.