Agree it's possible the batteries are the same, but I think it's equally likely they have a better spec for the 600/700 battery. It's possible that the 600/700 lights won't meet spec (brightness, run-time) with the lesser battery. There would be no need to key it differently as the batteries are not incompatible, but might only provide lesser run-times at the higher current draw of the brighter lights, or have higher ESR that could limit max brightness. ...but maybe not.