IMO they are Sony VTC4's. Illumination Supply is a known good battery vendor and will not sell counterfeits. I would say you're good to go
Hello Ryedan. First let me say I enjoy your posts but in this specific case I beg to differ.
There is a post around here somewhere speaking of how efest sent them an email regarding this, something about only 3900 or so efest purple 2100mah being rewrapped Sony VTC4. I may have the exact number incorrect but you get the gist. Anyway, about 2 weeks ago I ordered a couple of them from Illumination Supply and four Sony VTC4, 2 from Lightning Vapes and 2 more from an Ebay seller.
I also picked up one efest purple 2500mah, "so called" 35amp from Illumn and 2 Samsung 20-r, 2000mah from RTD Vapor. I usually run VTC4 exclusively so I know exactly that on my Reo with a .9ish to 1Ω coil, checking my V-drop at the atty post under load will give me .21 vdrop everytime. So I charged and loaded up each of those new batteries and the results were as follows:
Ebay VTC4 .21 vdrop
LightningVapes VTC4 .21
Efest Purple 2500 .22
Efest Purple 2100 V1 flat top .23
Samsung 20R .23
Samsung 25R (used) .24
The Samsung 20r was a disappointment as I held out higher hopes for it. Pleasantly surprised at the Efest 2500mah but I was also really hoping the Efest 2100 were rewrapped vtc4 but the vdrop got me curious enough to pull out my razor.
View attachment 395272
Both are the new batteries. Notice there are is no Sony printing anywhere on the Efest. The battery is bare of any markings at all.
View attachment 395273
Notice the difference in the positive cap. The Sony is known for it's 3-pronged cap, much like the Samsung 25-r but the Efest 2100 has a 4-prong cap.
By this point I'm convinced they're not rewrapped vtc4 but as a final test I placed both in my Opus BT-3100 charger/analyzer for an internal resistance test
The VTC4 repeatedly came up reading 39-41ish milliohm.
The Efest 2100 kept giving me an average of 80. Almost twice the ir of the vtc4. As I'm sure you know, the vtc4 have quite the reputation for low internal resistance.
I'm not insinuating the efest 2100 are bad batteries, nor is this a jab at Illumn Supply. No where on their web page do they claim the efest are rewrapped VTC4. As a matter of fact, they vape fine at the higher resistance I prefer but... VTC4? I don't think so. Unfortunately, I'm not equipped to run and chart discharge curves but imo, the markings, top caps and IR readings equal compelling evidence.
Now if you friends will excuse me, I need to go rewrap some batteries.
cheers
Hello Ryedan. First let me say I enjoy your posts but in this specific case I beg to differ.
There is a post around here somewhere speaking of how efest sent them an email regarding this, something about only 3900 or so efest purple 2100mah being rewrapped Sony VTC4. I may have the exact number incorrect but you get the gist. Anyway, about 2 weeks ago I ordered a couple of them from Illumination Supply and four Sony VTC4, 2 from Lightning Vapes and 2 more from an Ebay seller.
I also picked up one efest purple 2500mah, "so called" 35amp from Illumn and 2 Samsung 20-r, 2000mah from RTD Vapor. I usually run VTC4 exclusively so I know exactly that on my Reo with a .9ish to 1Ω coil, checking my V-drop at the atty post under load will give me .21 vdrop everytime. So I charged and loaded up each of those new batteries and the results were as follows:
Ebay VTC4 .21 vdrop
LightningVapes VTC4 .21
Efest Purple 2500 .22
Efest Purple 2100 V1 flat top .23
Samsung 20R .23
Samsung 25R (used) .24
The Samsung 20r was a disappointment as I held out higher hopes for it. Pleasantly surprised at the Efest 2500mah but I was also really hoping the Efest 2100 were rewrapped vtc4 but the vdrop got me curious enough to pull out my razor.
View attachment 395272
Both are the new batteries. Notice there are is no Sony printing anywhere on the Efest. The battery is bare of any markings at all.
View attachment 395273
Notice the difference in the positive cap. The Sony is known for it's 3-pronged cap, much like the Samsung 25-r but the Efest 2100 has a 4-prong cap.
By this point I'm convinced they're not rewrapped vtc4 but as a final test I placed both in my Opus BT-3100 charger/analyzer for an internal resistance test
The VTC4 repeatedly came up reading 39-41ish milliohm.
The Efest 2100 kept giving me an average of 80. Almost twice the ir of the vtc4. As I'm sure you know, the vtc4 have quite the reputation for low internal resistance.
I'm not insinuating the efest 2100 are bad batteries, nor is this a jab at Illumn Supply. No where on their web page do they claim the efest are rewrapped VTC4. As a matter of fact, they vape fine at the higher resistance I prefer but... VTC4? I don't think so. Unfortunately, I'm not equipped to run and chart discharge curves but imo, the markings, top caps and IR readings equal compelling evidence.
Now if you friends will excuse me, I need to go rewrap some batteries.
cheers
. I made some assumptions and you know what people say about why that's not a good idea! 
