24 across
Final
points,
one
of
which
is
negative
in
its
conclusion
(7)
Final points, one of which is negative in its conclusion (7)
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The whole clue is the definition (& lit or double definition).
How the clue works
The whole clue is a cryptic definition: terminals are 'final points', and on a battery one of them is the negative terminal — its 'conclusion'. There is no separate wordplay component, just the whimsical description pointing to TERMINI.