What is Kelvin Sensing?
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Wire resistance
+--------+
¦ OUTPUT¦=======/\/\=======+
¦ ¦ /¦
¦ High ¦----------------/ ¦
¦ Sense¦ Kelvin lead /
¦ ¦ \ LOAD
¦ Low ¦ Kelvin lead /
¦ Sense¦---------------- \
¦ ¦ \ ¦
¦ ¦ \¦
¦ RETURN¦=======/\/\=======+
+--------+
When you pump current through a resistance,
you get a voltage drop across that resistance.
In a power system, you want to sense the voltage at the load
and adjust the supply's output level
to get the voltage that is actually delivered TO THE LOAD correct.
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How this relates to your original question:
When a car starter pulls >100 amps,
the voltage drop across the internal resistance of the battery is
significant.
When a LED pulls 0.020 amps out of the battery, the drop is nil.
To get an idea of what a condition a battery will be in
to deliver starting current,
you have to pull significant current out of the battery.
As DBLEXPOSURE has pointed out,
to do so continuously will, of course, run down the battery.