you could try the protected AW17500 battery (lighthound carries them) or the Wolf Eyes LRB-150B (pts-flashlights carries them), but they won't give any more
punch than the AW IMR14500. the difference is that it will give the same punch for a
longer period of time, because each of these
batteries is able to handle the desired amp draw, but the lithium cobalt
batteries are able to provide more energy density based on chemistry and size. both of these AW and Wolf Eyes consistently come in at under 17mm in diameter, similar to the AW17670 in the GGTB, so if the diameter of that cell fits the Grant but the length doesn't, then either the AW or Wolf Eyes "17500" batteries should fit just fine as their length won't be longer than stacked CR2's.