The charger should have had a listed output current somewhere. Most of the older type where 500ma.
The voltage the led is runnig at is also directly related to the current. Just like when a battery voltage decrease in direct drive so does the current.
You can’t have a certain current unless you have the correlated voltage.
Heat build up can sway that a little or certain bins have lower vf’s but we use these graphs as a guide for a particular led.