Don't worry about the voltage difference. Both sizes are approved by Dell, as can be seen in Dell's specifications for your laptop.
Hi,   I just bought a Precision 7530 with an almost dead battery. Looking for a replacement I found out that there are 2 sizes available: 7.6V 64Wh and the larger 11.4 97Wh. I have the 64Wh version but I wondered if I could get the 97WH and install it as a replacement for the 64Wh. The difference in voltage made me doubt if this is even possible without frying the motherboard. Btw.: (7.6 devided by 4 (64Wh cells) times 6 (97Wh cells)=11.4. Hope someone could clarify things 
Precision 7530 Battery replacement