I have bought a second Xbox one S at a super new price as a reserve and now the question may be broken if it is not used for years but is in original packaging?
If you keep them dry, the device will last for years, if not decades, but I advise you to store anything that has such a high loss of value as the XBox. At the end of next year you will not even get 20 euro for it
I do not want to sell it but keep it as a reserve if the other one breaks down
Yes, you have to store well and do not put it under the hot roof. In the basement. But bad idea to put a console on the shelf as a reserve. Buy rather new in the market when the old one is broken. In the meantime everything develops further.
If you have a Vacuumiergerät, or one in the family circumsatizes the thing, but a functional test would be appropriate before.
Then unpack every 2 years, recharge and test.
That's a waste of money, even if it's broken in 4 months, you could buy a new cheaper than the price you paid now.
And that does not just break, you'll stay on the newly purchased device until it's worthless.