Can we use the flashlight while it is being charged at the same time? Is it not recommended by Olight?
Yes, as discussed above, it is hard to know how the circuit handles charging while the light is on. The light does run with the charger cable plugged in - but it's unclear if that will give you any additional benefit for continuous runtime (or how much).You can, but the light is still running off battery, not the charge trickle. You might get 10-20 minutes more runtime while charging (don't quote me on this)
As a general rule, it is better to charger Li-ions without a current draw being applied at the same time. This can be confusing for charger circuitry, as the batteries don't behave the same way as when there is no current draw.