Generally, you want to stay between 20 and 80-90% charge on Lithium cells to prevent dendrite formation, which rapidly degrades the cell.
That being said, most cells are rated at about 1,000 cycles or so. A cycle is any time the chemistry is forced to reverse and store a charge vs discharge. So, be it a full charge of 1.5ish hours or ten seconds on a charger before you pull it off, that’s a cycle.
Light users consume 1-2 cycles a day, or 3+ for heavier users, so 1-3 year life is not abnormal.
Like Maymne recommended, Accubattery is incredibly good for figuring out cell health by watching your charge/discharge cycles and patterns, reported charge/discharge rate, estimated vs actual runtimes, etc. A few days of using that should help you suss out if the cell has degraded or not.