If it refers to the fast charge itself, then it does have harm to the battery, but this damage is negligible, and the benefits obtained are far greater than the damage itself. If it means that 20w exceeds 18w will there be additional damage to the battery, as long as you use a regular charger, there is no problem, the charger will dynamically adjust the power according to the situation of the battery, and will not be charged at 20w power all the way.
No, 20w is a match,