Balls, wrote a whole reply, hit [preview] to edit it but never [save]…
Anyway, that’s normal.
See post #2 from here Ultrafire DV-S9 diving light? .
The Hall-effect sensor drains about 10mA, so if using, say, a 5000mAH cell like my blue-wrapped LKs, that’s
5000mAH / 10mA = 500H
or about 20-21 days, spot on.
They lock out with a fractional-turn of the tailcap, so that’s what I do ’til I need to use it.