After a day with my SiD - I'm not sure if its my battery or the device, but after the battery drops down to about 3.8v the device nolonger works - nothing shows up on the display, pushing the button does nothing. The battery is a cheap BFN 18650 2200 mAh. It comes off the charger at 4.1 or 4.2. Come to think of it, I think its the battery (protected) saying 3.7 on the side.
Also, the device resets to what I would assume is factory settings after taking out the battery and replacing it after it is charged (I only have 1 battery right now, more in the mail, should arrive today!!). From other reviews it seems its supposed to remember your wattage setting and (i think) what mode you were in (vv or vw). I removed and quickly replaced the battery after a full charge and still this behavior exists.
I'm not sure if my SiD is a Legit SiD because it does not have the "SiD" on the battery tube. All of the functions of the control head seem to be the same as other reviewers have showed (aside from removing the battery). The box it came in seems to be the SiD retail box, but I have nothing to compare that too.
I'm still really happy with the device, but I wanted to let others know who may be considering a purchase of one of these. I bought mine from a vendor I had not used before because they had an excellent price. I'm sure if I used my usual vendor (and paid $15 more) I would be much happier with the rubberized version of the SiD.
It has not failed on me - button works 100% of the time. My Kanger Pro Tank Mini 2s and Vivi Nova work well on the SiD. I cannot unscrew my tanks grasping the base of the tank (without removing the beauty ring from the SiD) so I find my self paying close attention to make sure I'm not unscrewing my tank into multiple pieces... (exposing the juice compartment). Hasn't happend yet, but I'll continue to be cautious!
