That I don't know. I only have one EI engine (a Fuji) and I'm still using the 4.8v pack that came with it. It's a little bugger - four of what I guess are "1/2A" size cells rated at 1400mAh total. The manual says: "The ignition module runs on any 4.8V battery". Not sure what 6.0V might do, but why risk it? Sometimes more is too much.