iPhone SE 2020 - does not hold charge when powered off

Hello,

I have an iPhone SE2020 that when fully charged, then powered off (NOT put to sleep), does not hold charge for even a week. This is my work phone, which I rarely use, but every Wednesday when I work from home I pick it up and go to turn on and it is dead. It is on iOS 14.8.

Granted I am not overly concerned about it, but just curious on how long should the battery actually remain somewhat charged after 7 days of powered off and not used AND why would it be dead after a week of just sitting on my desk.

From a search on here, there are older reports of other iPhones that won't hold charge but those are all about they use their phones often and the phone doesn't seem to hold a charge for as long as the specs say they should.

Thanks!!

Jim