Only if the system is online. While that might be the case for most users, Sony designs their hardware with the consideration that it can be used offline. Considering the unit cost of a PS5, and the fact that backup batteries are already the norm, including one isn't imposing at all and there is very little reason to stop.
Inventing software solutions to already solved problems (and ones that don't pass all use-cases) isn't really a path worth going down unless the savings are actually significant.
No. A coin cell wouldn't be used for anything more complicated than keeping a simple real time clock chip powered. Is it possible? Sure, with a level of engineering effort that would far outweigh any possible benefit.
If they had something fancy they wanted to do on battery power, they would stick in a Li-ion battery, which they didn't.
I guess I wasn't super clear. Also, obviously the system is powered on when any disc reading is happening.
I was thinking about the issue with key expiration dates and validation. It's not a good user experience to force users to enter the current date every time they boot their offline system.
Didn't Macs have trouble booting if the clock is wrong? IIRC because from the system's point of view some cryptographic certificate's validity is in the future...
Yeah, that's the problem you want to make sure users don't face every time they power on their device.
Guessing: Perhaps, after Fukushima, Japan, like Germany has become very conscious about allowing people to completely shut off their devices when they are not using them?
I do remember German computer mags being very concerned with standby/operating power usage already like 15-20 years ago for things like home routers.
Button cell clock batteries have been a thing in most computers since at least the 1980s (including in every previous Playstation console that has an internal clock, PS2 and up), so it's not that unusual to see one in the PS5, and I don't think influenced by anything recent.
Perhaps it's primarily for validating signatures from discs in an offline scenario.