The issue is not the battery per se. The issue is that supplied battery has been modified, so that both the + and - connections are on the same end. The flashlight will only operate at the highest power levels if it detects that the negative terminal in use is at the top rather than via the spring connection at the bottom. At least in theory you could modify an existing battery to put the negative terminal on a ring conductor at the + end of the battery. One of the things that was accomplished with the negative connection at the top end is the conductor area is huge relative to the size of the conductor on the other end (take a look inside the light, and look how the ring on the top of the battery connects to the flashlight. It uses almost the entire area of the ring conductor at the top of the battery). The standard negative connection is simply your typical spring. This very large area conductor makes it much easier for the battery to deliver higher currents