7.4v lipo's come off charge at 8.4v 8.4v come off charge about 9.3v anyway 9.6v come off charge at 10.4v
tbh either will bo ok but 9.6v is max I'd run without fet. Main problem is possible space for battery. lipo's I'd say can be more compact than nimah's
Just go lipo - they are usually cheaper and size options are quite varied so you should get something to fit in almost any gun - 7.4v lipo equates to a 8.4v but has more grunt especially in a tweaked gun
