The Samsung 25r are 20 amp continuous discharge rated batteries, and would be a 33% reduction from the recommended rating the mod manufacturer lists. At higher watts you would be likely pushing them over their rated amperage which could ruin your whole day.
Consider if something goes wrong, you have 2 batteries that could vent, so double the failure, right next to your face. I would say stick with the recommended batteries and shop around. I have a local B&M that had the VTC4 & VTC5 at reasonable prices, even after it was reported many online stores were out of stock. I checked them six ways from Tuesday for authenticity and they passed all the tests. Either the perfect clones of real VTC batteries.
It is true that the Samsung 25R is listed as a 20A continuous battery, but that rating doesn't really apply to a VV/VW device as it is my understanding that with many high wattage devices out now accidentally discharging the mod for the entirety of the battery charge is basically impossible. So, why bother with only looking at a continuous battery drain spec? It's prudent to choose batteries wisely and I would never argue with that but the current market demands that we take a bit deeper look into our options.
What many people do not know is that the VTC5 was never officially tested to 30A, even the Spec sheet has no mention of the VTC5 being a "30A continuous" cell, but it was tested very nicely at 20A. Independent outside testing has shown us that the VTC5 can perform well at 30A which is why we consider it a 30A cell, I can personally find no literature anywhere from Sony that shows the VTC5 being tested at over 20A. Where am I going with this?
Here is the Samsung 25R spec sheet -
http://www.powerstream.com/p/INR18650-25R-datasheet.pdf
That sheet shows continuous drain testing up to 25A and in the final few pages even demonstrates that the 25R can discharge well over 30A for short bursts without venting in any way. Safety testing looks very good as well, even under the most detrimental of conditions the battery at very worst only leaked, not a single test cell once vented anything violently and the cell retained an L1 rating throughout all tests, scoring an L0(the best rating) for some of the tests as well!
My point in all this is that independent outside testing has also shown the 25R can output 30A reliably along the near same discharge curve as the VTC5. Now in my eyes it's up to the user to decide if they're informed enough to make a decision on using the 25R for higher discharge, personally it's now a battery I have my eyes on to purchase more of.
