How tight ba dapat yung mga belts particularly yung alternator belt? How much "free play" when I press on it is tolearble?

I am experiencing a small drop in idle when I have my aircon on and i open my headlight. Yung sudden electrical load na yun causes my idle to drop pero nag-iistabilize naman sya, may drop lang na noticeable. or baka siguro medyo oc lang ako kaya noticeable, hehe.
My self diagnostics or hula is baka the alternator is not pumping enough juice to charge my battery. Battery was replaced a few months back before I had my aircon cleaned where they took down everything including compressor so apektado belts???

san ko ba pwede to pacheck? Accord nga pala and battery is motolite excel 2sm, yung green.

thanks