I replaced the battery in the Istick 20 W. The maximum current draw from the battery in the iStick 20W is 5.5 Ampere.
The battery installed in the iStick is a cilindrical Li-poly of good quality, with 50 milliOhm internal resistance. It is marked "18650" but in reality is a 18630, it is two millimeter shorter than a standard 18650. In any case the shortness is taken care with sticky foam pads, so a standard 18650 cell will properly fit the iStick 20 W.
The Panasonic NCR18650B is a hybrid LiNiMnAlCo cathode, graphite anode battery, rated at 2C - or 7 Ampere maximum continous current draw. Provided it is original, the NCR18650B makes the best absolute replacement for the iStick 20, as its maximum current rating is lower than the maximum draw of the mod.
The iStick (and all mods in general) uses a smaller cycle voltage window than the NCR1850B is capable. This because the built-in Li-Poly cell is more delicate and is rated for much higher maximum current, around 15 Amperes, at the expense of cycle life. (Li-Poly are thermodinamically similar to Li-Co, which are bricked if brought, even briefly, below 3 V OCV). While you can expect 700 cycles with the Panasonic (if original), the original Li-poly will drop at 80% capacity after only 200 full cycles. For a normal vaper, charging the iStick every other day, 200 full cycles are one year and half. With the Panasonic 18650B, the LED display of the iStick 20W will be dimmed to nothing and the 510 threads will be ground to dust before requiring replacement after five years of use. Please note that, because of the reduced cycle window, the NCR18650B will behave more like a 2600 mAh battery. Also consider that the NCR18650B contains a PTC protection which brings the total internal resistance to 100 milliOhm. I kept account of this when, above, I stated that the battery behaves as a 2600 mAh battery. The PTC adds a notable layer of safety, should to iStick be subjected to an electrical or mechanical incident, or abuse.
In the iStick 50 W, the NCR18650 is not suitable. Li-Poly remains the best choice for that kind of power. I think they can be sourced directly in China on Alibaba. In any case, hybrid 18650 cells will not work safely. Only Li-Mn batteries of know quality (AW preferably, I would say are the ONLY choice) can be used to replace the Li-Poly cells in the iStick 50 W. In any case, it is a problem that you will face in 18 months time. For the time being, I am now buying only mods with replaceable cells, to avoid future headaches.
