I don't think you can answer this question without knowing the optional equipment in the front of the CG and the weight of the pilot and copilot
Do a W&B to get your answer ( deduct the weight and arm difference from the old battery )
Also remember the arm of the baggage is somewhat under your control.
When the fore-aft center of gravity (CG) is out of range serious aircraft control problems occur. The fore-aft CG affects longitudinal stability of the aircraft, with the stability increasing as the CG moves forward, and stability decreasing as the CG moves aft. With a forward CG position, although the stability of the aircraft increases, the elevator control authority is reduced. This can cause a serious condition during the landing flare.
A good read
Originally Posted by engineerofsorts
Having done a good "scratch and sniff" on the RV-12iS at Oshkosh, I came away very impressed with the refinements.
Also, having hefted the normal battery and an EarthX battery, I came away lusting after the potential weight savings if I could plunk one of those into my now-"classic" RV-12. Since the batteries are not physically identical (EarthX battery's terminals are in different positions than the 680) a bit of massage of the battery holder would be needed. However, CG-wise, the lighter battery forward of the CG seems like it it would have the effect of lessening the max luggage capacity aft of the CG. Ten cuss words if my analysis is correct.