There’s an explanation of the pre-order issue here: Efficiency measurements of a few drivers - #92 by thefreeman
Mine was from the pre-order and I had it before the above was posted (July 2023). So I figured mine had the flawed driver. Of course Zebralight never reached out to anyone so there’s really no way to know for sure aside from opening up the light. It always annoyed me, as well as the fact the tailcap spring cuts a groove in the battery. So, upon learning that they’ve addressed the tailcap spring now, and presumably addressed the driver issue long ago, I bought another.
To try and quantify how the driver change would affect runtime, I decided to do a runtime test with the same battery (not same type, same exact) on H1 since the highest levels are where this inefficiency is supposed to manifest most clearly. I used a cooling fan because otherwise just sitting they tend to thermally throttle. And here it is:
Note, I included a test of the SC54w HI but it was not done as recently. It did use the same battery but I did this test a year or two ago. I have tested my pre-order SC65 before but wanted to do it again so that its comparison to the new one had fewer variables. I don’t care to redo the SC64w HI test, but I think it’s reasonable to include. Back when I did test it, I also tested my pre-order SC65 and that looks basically the same as the test I just did.
So, I have no idea. Maybe my preorder wasn’t affected, maybe they never fixed it (though I’ve seen posts from McBob saying it was fixed), maybe it doesn’t actually cause much of an issue. Maybe there’s so much room for error in my tests that by random chance they ended up looking the same. Maybe that 10 minutes of 75 lumens at the end is the benefit from the update. Who knows.
It also really doesn’t seem like it’s an efficiency improvement over the SC64. But obviously the low CRI XHP35 has higher efficacy, so maybe the driver is pushing less power for the same time as the SC65, and if a 719a were swapped into the SC64 it would be a lower amount of lumens over the same time as the SC65 is managing. Who knows.
Finally, while the tailcap does have the spring bent at the end, it still marks the battery and sounds like there is gravel in the threads (which goes away when the battery is removed, so it’s probably not the threads). However, it looks more like it is polishing a ring in what is a somewhat stonewashed finish on the battery, rather than cutting a groove. When I used the battery from my old SC65 for the runtime test, it was a lot smoother to put the tailcap on than with the brand-new battery that the new light shipped with. So maybe once the ring is polished the tailcap might feel a lot better.
