NOTE: This method of choosing a battery is for experienced vapers, familiar with battery performance specifications, using Ohm’s Law, and how to safely choose and use batteries in an unregulated/mechanical device. A method for new vapers to use for choosing a better performing battery is in development. Choosing a good unregulated/mech device battery is harder to do than one for a regulated device. While you can use the Wh specs to pick out a great overall performing battery it won’t tell you which hits harder unless the capacity ratings of the two batteries you are comparing are close. If the capacity ratings aren’t similar then both a high-capacity long-running, but not hard hitting, battery can have the same Wh spec as a lower capacity shorter-running, but very hard hitting, battery. You wouldn’t be able to tell which was the harder hitter. That’s where the DC internal resistance spec can help out. While it can’t tell you which battery will hit the hardest for the whole time it’s used it can tell you which will hit harder at the start. So, if the capacity ratings are about the same then choose the battery with the higher Wh spec and you should get the one that hits harder...should. If their capacities are different then choose the one with the lower internal resistance if their Wh specs are similar. Be sure to use the Wh spec closest to the current level you are running your batteries at. It can make a big difference. Here’s another scenario... Let’s compare three batteries used often in mechs, the Samsung 25R, Samsung 20S, and Sony VTC5A. Which is best if we just have the internal resistance spec or a discharge graph? The basic specs are... Samsung 20S = 2000mAh 30A, 13.5mOhms DC internal resistance Samsung 25R = 2500mAh 20A, about 21mOhms Sony VTC5A = 2500mAh 25A, about 18mOhms NOTE: Don’t let the current rating fool you. It’s a spec related to cycle life (how many times the battery can be discharged) and safety, not raw performance. The LG HB6 is a 30A battery but the 20A-rated Samsung 25R still hits harder. The lower internal resistance of the Samsung 20S indicates that it would hit the hardest but its lower capacity might mean that its voltage drops before the others as you continue to use it. The numbers alone don’t tell us enough information so we’ll need to go to the discharge graphs. At 10A in the discharge graph you can see that the three plot lines are all kind of intertwined and fairly close together. This indicates that there’s no real winner. The VTC5A comes out slightly ahead overall but not by much. You probably wouldn’t notice the difference between them at 10A. But at 30A the difference in performance between them is striking. The Samsung 20S is clearly the best performer. It hits a lot harder (runs at a higher voltage) and runs for longer than the other two. This is due to its lower DC internal resistance. CAUTION: 30A is above the rating of both the Samsung 25R and Sony VTC5A and running these batteries at that level was done only for demonstration purposes. I recommend not exceeding the continuous current rating of any battery to help lower the risks of using them, help extend their life, and improve their performance. Even though the Samsung 20S has the lower capacity, 2000mAh, its lower internal resistance gives it incredible performance at higher current levels. The Samsung 20S would actually run for about twice as long as a Samsung 25R at 30A, even though the 25R is a higher capacity battery! It’s easy to pick out the winner when they’re directly compared like this in one graph. What do you do when the DC internal resistance spec or a comparison graph like this doesn’t exist? Look at the discharge graphs in each of my test reports and choose a voltage like 3.2V. It’s a common stopping point for mech users because it results in a battery at about 3.6V when you stop and the battery voltage rises back up. Slide right along the 3.2V line until you hit the discharge plot line closest to the current you will be drawing from the battery. Then drop straight down and note the mAh the battery delivered. Do this for each battery. The battery with the highest delivered capacity will probably be the best choice. While not a perfect method it should get you the battery that will hit the hardest for the longest. So, while it’s definitely harder to pick the best battery for an unregulated/mech device there are several ways, most fairly simple, you can narrow down the choices. If you get stuck, please feel free to ask me which batteries you are considering might be the better choice at the current level you will vape at.