55 amp Alternator & double v-belts

[awolff280sl]

In the workshop manual for the 280SL, in section 23-2 re: tensioning of V-belts, there is a subsection on V-Belts for 55 Amp. Generator. This applies to other models that were originally equipped with a 55 amp alternator. In this subsection, mention is made of a second water pump-alternator belt. This is in addition to the long crankshaft-alternator-water pump belt.
Some of us W113 owners have replaced the original 35 amp alternator with a 55 amp, and looking through the forum there has not been any mention of using an additional belt.
Does anyone know the purpose of this 2nd alternator belt?
FWIW, I am using a 55 amp internally regulated alternator on a single crankshaft-alternator-water pump belt. I have seen that my alternator usually puts out an average of about 13.4 volts (13.2-13.6).

[Cees Klumper]

Not an answer, but two follow-on questions: why move to a 55 amp alternator, and does that require a different battery to function properly?

[awolff280sl]

Cees, 55amps in my car is not entirely necessary. It would be needed with a monster sound system. I put it in when I re-did my water pump, A/C, etc. because I was there.
I don't need a different battery.

[Naj ✝︎]

When I bought a 55a alternator for my Pagoda, it came with a double belt pulley of much smaller dia. I just swapped the pulley from the displaced alternator. I do not think you need the double pulley.
I fitted a 70a alternator on another Pagoda with a single pulley. The belt chirps every time after start up.

Naj