Considering that the majority of available phone batteries are either Li-Ion or Li-PO (3.6 or 3.7 nominal voltage, 4.1 or 4.2 fully charged), and neither type suffers from memory effect, there is no need to perform any special acrobatics.
That said, lithium rechargeables have a recommended storage voltage level (about 3.84 volts or somewhere around 40-70% full), at this charge level they age much slower. This is why batteries in new products are typically shipped at about 60% charge and not at 100%. A fully charged or fully discharged battery will age more quickly (fully discharged is the worst long-term condition).
Unfortunately, many products such as backup battery packs, flashlights, etc are most useful when they are kept fully charged and ready for action – thus we sacrifice longevity for convenience.
People with expensive lithium battery packs (larger radio-controlled air craft, for example), keep their batteries at storage level (3.84V) and in the refrigerator where their longevity is maximized.
If you keep it out of freezing temperatures and keep a battery tender hooked up to keep it charged it should be fine for several years.
Hi it needs to be kept charged so it needs to have a battery charger attached and it needs to switched on.
Check expiration date
Store it off the floor and charge it monthly and it will last a year.