i know this might not be the right forum but i need some experienced help here

battery dies every 4-5 weeks...replaced battery, checked grounds and checked alternator...all fine

i get 12.45 volts at the battery while at idle
while driving, while headlights and dashlights dim and go bright like 20 time a minute...can anyone help me?

ive heard of the ELD going bad (electric load detector)
also, when my a/c kicks in, it bounces up like 200 rpms and settles down
ive replaced 3 batteries in the last year...could it be my regulator?...shouldnt it be 14.4 volts at idle?
help guys please

jman