Useless? No.
Capable of being driven WAY past it’s intended operating parameters with a single cell? No.
Some cells do maintain higher voltage during their discharge curve than others - Cells like that will drive it harder.
uselss i ment if you want to drive it 4.5 amps or more,thanks for your help.
I've had no problem getting/maintaining 3.85 or 4.2A with a single Samsung INR 2000 or Pana PD with a tailcap reading. Are you measuring at the SinkPAD?
Do you think a 4.5A driven XM-L/alum star will be brighter than a 3.5A driven XM-L2/SinkPAD? I'm thinking not. I had a 7G9 mod'ed that way at 4.5A and it was a pretty useless configuration. An XML at 4.5A on an alum star is not very productive. Light meters can really take the guess work out of it.
i measured at the cap, ijust wanted to see how bright will be,i wanted to make 4,5A on copper sinkpads,the same VF rule applies for the XPG2 as well? or is it the same as the xpg1?
The XPG-2 is actually the opposite. It has a lower Vf than the original XP-G, so it will pull MORE current from the same cell.
You’re probably correct, but I’ll bet an original XM-L on a SinkPAD at 4.5ish Amps would be the brightest of them all. That’s just a guess though, I’m not looking at any data to backup the claim. It’s a good bet though.
Well the SinkPAD's make the XML or XM-L2's run a lot cooler at higher amps, so my thinking is the SinkPAD drives up the vF, maybe more than the difference between an XML and XM-L2. In tests I've done between a XML U3 1C on a SinkPAD and an XM-L2 U2 1C on a SinkPAD both at 3.85A, the measurements had the XM-L2's higher, but it wasn't a fair comparison because of different hosts - UF C8 vs. a SupFire X5, similar lights though.
But what do you think, even for a normal resistance unprotected cell that can't do the max amps, isn't the vF still higher so total power is the same (almost) compared to a XML/alum star that it can do the max amps? Again, total power (W = V * I) of course you know that 
. Or is it truly losing power? Maybe somewhere in between?
do the math, i posted a spreadsheet about it in some thread, here it is again
In match’s tests the xm-l2 was performing at equivalent to 25ºC, but he had lots of heatsinking
Total Power for an LED is a bit strange…
The amount of heat generated and electrical energy consumed is P=V*I, but LIGHT output is only related to I and T (Current and Temperature). In terms of light output, you don’t care what the Vf is - only what the If and temperature are.
Where did you buy the copper sinkpads?
Originally from the group buy nitro organized, now buying from VOB (vestureofblood) - he's got a cpfmarketplace page. Just got an order of 10 more in my hands that came today, along with the custom copper pills! Thanks VOB!!