I believe it's right at 4 V that the circuit cuts off. So you may get some output, very briefly. Soshine LFP cells are going to be your best bet. Or K2 if you prefer but the soshine are easier to get. I'm not sure what it's like with other colors, but I know that with my red secondaries, you can really see them in the main beam if you're using IMR cells. I'm not saying it's going to damage them long-term I have no idea, I just know that it makes them too bright. With the LFP cells they are brighter than with primaries, but not by much. But the nice thing is they stay that same output from fully charged to dead just because of how flat the discharge curve is of that chemistry.