You'll love the LR's at 3.7 volts, but I'm afraid the 510 cartos may be too weak at that voltage. I think 6 volts is too high, though, but some people don't. The reason they're telling you not to use the Omega at 6 volts is basically just to cover their owns rears about possible battery problems by stacking batteries. If I'm not mistaken, they may have encouraged 6 volt use before a few people were reporting battery safety issues. Many people use them like that without problems, but there's always a chance.