A Nintendo Support X post explaining to consumers that consoles and similar devices which include a Lithium-ion battery need charging once every six months has gone viral in The Land of the Rising Sun. The informative post should prove to be a wakeup call to those of you who have older handhelds etc stored in cupboards throughout the world that they need booting up and charging every now and again to make sure that they can retain their charge going forward.
“Lithium-ion batteries built into game consoles and similar devices may lose the ability to retain charge if they remain in a state of neither charged nor used for an extended period of time.
Make sure that you charge the product at least once every six months”

I always have my Nintendo handhelds charging, mainly because my 2ds makes the brightest flashing light when it’s dying and it’s extremely annoying.
May I take a moment to remind people of the PSP Swollen battery tweet that made the rounds a few years ago, and also check to see if your battery is swollen before charging
I think I have most 3DS models, and I have a multiday session charging them a couple of times a year xD
I recently changed out all of my batteries with high capacity ones. I still love using my Animal Crossing 2DS with a DSpico flash cartridge.
I make sure my DSi always has a charge. I just started playing through Custom Robo Arena for the first time in years so I’ll definitely be needing it to power on for the next few days.