I have also noticed that the H51 uses the same thin battery spring as the H501. I hope Zebralight will use a thicker and stronger spring for the H502 like the one they use in their bigger lights. Adding a magnet to the tail cap greatly enhances the versatility of a my H501. Unfortunately, the magnet was strong enough a pull the battery toward the tail end of the light. Eventually, after about 8 months of this stress, the spring weakened and the battery stopped making contact at the head of the light. For the H51w, I weaken the magnet's impact on the spring by putting a penny between tail cap and the magnet.
If it took 8 months of repeated stress to have an impact on a pretty thin contact spring, I am sure a thicker and stronger spring like the one used in their big lights will prevent this problem from occurring.