Waxxy, you seem to be mixing up your Mag mods. The ROP uses the Pelican Big-D SLA bulb, which is best driven using 6 NiMH cells, or 7 if they are well-rested. 9 NiMH cells in a Mag is almost certainly a Mag85. This uses a Welch-Allyn 1185 bulb. However, it is a bi-pin bulb, so you need an adapter, or one that has already been potted to fit into your Mag 3D.
Of course, many have tried. The most common version is called the Mag85.
You could also fit 12 AAs(correctly sized/positioned batteries or a quad bored Maglite), 3 Li-ion D Cells, 3 18650 batteries, 4 C sized cells, and many more combinations in a Mag3D. Even more if you have a bored Mag 3D.
If it popped at 8.6v, then it probably won't be able to handle 10.8v