How Long do New Unused switch system’s Battery life last?

[LimitBreaker420]

So I have a couple switches that are brand new and unopened, I recently started collecting them and I’m curious to know how long can they last, battery wise, if you never open them and use them. Does anyone have an idea.

 

[thesjaakspoiler]

This site says that it's about 4 years :
https://www.batteryuniverse.com/blog/tags/shelf-life/

Also if you start charging them, charge them up to 80% instead of 100%.
Leaving lithium batteries unused with a 100% charge is also bad for the battery condition.

 

[FAST6191]

Varies with temperature of course (my cold garage or hot attic probably being worse than a nice room temperature setup).

Anyway don't know the quiescent current and self discharge rates of a Switch (especially not an unopened one) and I am not sure anyone really does. That said the site above is a reasonable estimate for an average setup.
It would also depend how far into deep discharge you care to wander*, and your recovery options when you do.

*a basic battery that you might have done when you were 6 with a copper and zinc strip in a lemon or maybe potato is much like normal batteries, however rechargeable batteries make a slight twist with "half reactions" that you can go back and forth between quite easily. Discharge it too much (deep into the discharge curve if you will) and these half reactions become full reactions which are hard to recover from without more specialist setups that are not typically onboard devices in any really meaningful capacity (though some have the barest whiff of it these days). Lithium chemistries used thus far in consumer devices being especially prone to this (actually more so than a lot of older ones) but lithium has other perks so it continues to be used.

If this is some kind of "still in the shrink wrap" ploy for the later resale market then that gets complicated as many fields have now been seen to respect those that do some kind of preventative maintenance on their batteries (pokemon being the most surprising for me on that one). Whether this takes the form of opening it (naturally smallest possible cut, or maybe least visible cut, to the shrink wrap to open the thing) to charge every so often, removing the battery entirely to keep that charged separately, making a hole in the box to charge it (there is probably a nice direct line to it after all), opening the thing but adding a wireless charger to mean you don't continually open it in the future or something else that ensures your battery is in the best possible condition when others will have rotted is up to you. It also presumes none of the nice lead free solder joints, heat paste or whatever don't similarly degrade with time for another issue there.
I am also expecting if not custom batteries (though I am expecting those like we have custom PCBs today) then future battery tech to be able to outright replace things (even if you have to have a secondary board in there to make the host console believe it has an original style battery** if the replacement still ends up with more than the theoretical max then is there much benefit to future battery). In which case we get to contemplate puffy batteries (which might blow out the case or screen) and leaky batteries (less of an issue than older ones that kill xboxes, amigas and my recent vintage PC find) instead and is way less of an issue with the ones that remove the battery entirely as it is presumably sitting there doing its own thing outside the box or otherwise isolated.

**for as much of a faff as the whole constant current, temperature sensing, voltage measuring and whatnot of recovering from deep discharge is then normal charging is not without its quirks that various onboard devices will play to. This is also why you want to ensure the chemistry of your battery matches the chemistry of the charger if you want the best results (lifetime, charge speed which might be mutually exclusive from lifetime***, occasionally not being on fire...).

***see trickle charge and why you might want that. Or more generally why having nice fast charge on phones is great and all but why using it will kill your batteries in reasonably short order compared to not.