OK, so on Page 4 they claim:
ATTENTION: The Battery Tender® Plus CHARGER HAS A SPARK
FREE CIRCUITRY. The output alligator clips or ring terminals will not
spark when they are touched together.
Then they have you attach a 24 inch long lead as a:
FOLLOW THESE STEPS WHEN BATTERY IS OUTSIDE VEHICLE. A SPARK NEAR
THE BATTERY MAY CAUSE BATTERY EXPLOSION. TO REDUCE RISK OF A
SPARK NEAR BATTERY:
a) Check polarity of battery posts. POSITIVE (POS, P, +) battery post usually has a
larger diameter than NEGATIVE (NEG, N, –) post.
b) Attach at least a 24-inch-long 6-gauge (AWG) insulated battery cable to NEGATIVE
(NEG, N, –) battery post.
Sounds like their lawyer made them put this in...