Key seems to be charging it to only 50% and turning it off and storing it in that state, with a recharge back to 50% every 6 months (you do remember to set an alarm for that?).
But, as the article suggests, if you are going to store it for a year or more without using it, maybe you should consider giving it away or selling it rather.
See https://www.zdnet.com/home-and-office/how-to-store-your-old-smartphones-and-tablets