Or... if you like the Eleaf brand like I do, I'd suggest getting an Eleaf iPower 80W. This has a 5000 mAh battery life (even when I use it a lot), I only have to charge it around once a week. Personally, I like not having to use external batteries. In some, you will want to keep the two that go into the mod together, get an external battery charger, a case for storing the batteries for safety when not in use... even though I have all of those things and over a dozen paired batteries, it's more convenient for me to use the mods that have the batteries contained.