The 30amp fuse is only if you are re-wiring the RR direct to the battery.
Old or new battery will not affect your measurement with engine running. 12.4 on a battery is a minimum level of charge for a lead acid. Lead acid batteries like to be kept above 80% charge (12.5) or their life is greatly shortened.
My Measurements with re-wiring and upgraded MOSFET R/R:
13.2 ignition on not running
14.1 idle
14.4 over 2000 revs.
Cheers, Richard
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09 America, Staintune Pipes, K&N, Breathe, Hagon Nitros, AI & O2 removed, tune 20184 (modified), MTX-L a/f gauge
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