The definitive method to probe the device operating current
A current meter in series between the device and the power supply is the correct way.
You have to provide the proper voltage and current to the device for it to power on and operate normally.
The resistance mode of a DMM can't supply the correct current or voltage to the device so it doesn't actually turn on and operate.
The current you measured with the meter in current (ampere) mode is correct.

Modern devices might not be simple to measure.  They turn on and off, and &quot;take naps&quot; to reduce the total power consumed.
For that kind of thing you may need special equipment to measure fast changes in the current.
For a simple &quot;how long will my LED torch run on batteries,&quot; a measurement with a DMM is adequate.