Manual vs Automatic Batteries - This is as simple as it sounds. A user either presses a button to activate the device and begin vapor production (manual battery) or the user simply inhales to begin producing vapor (automatic battery). The choice of which battery type to use is yours, though more and more users prefer a manual battery these days. Some take advantage of the manual button by pressing it perhaps a half second or so before beginning to inhale which results in pre-warming the nicotine liquid before the device gets to the mouth.
Standard Sized Batteries - Regular or 'standard' size batteries are those that many consider to more closely resemble a real cigarette (in the industry a real cigarette is known as an 'analog' cigarette). New users often start out desiring smaller sized batteries based on looks. Examples in this class include the 510 battery (arguably the most popular in this size) as well as the NJOY NPRO (also known as the RN4081). Others include the Penstyle (otherwise known as the DSE801) and the DSE901. Many of these users find themselves upgrading to high-capacity batteries over time as at around 180mAh these sized batteries typically last under 4 hours or so before requiring a charge.
High Capacity Batteries - Higher capacity batteries are often longer or thicker than a real cigarette and will last much longer than standard sized 180mAh batteries, sometimes as much as days at a time depending on battery size and usage. Typically they will start around 350mAh and increase in size from there. The most popular high capacity battery is the eGO battery which comes in 350, 650, 900, 1100, 1300mah, and even up to 2200mah! High capacity batteries also allow for the use of many eLiquid tank systems not available for smaller standard capacity batteries.
Variable Voltage Batteries - Higher capacity batteries sometimes feature what is known as 'variable voltage' or VV. This allows users to twist a dial on the battery to adjust the voltage output of the battery. High voltages mean hotter vaping temperatures and thus more vapor and throat hit. This can be especially helpful for the occasional poor performing cartomizer or coil head or one that has been fading slowly over time. The downside can be burnt taste or shorter coil lifespan if too much voltage is used.
Passthroughs - A true passthrough is a something that might look like a battery but in fact is not. You screw your tank, cartomizer or atomizer onto a passthrough, and the other end is connected to a USB cable which plugs directly into a USB adapter or your PC or laptop. It allows you to vape all day without requiring a charge - since there is no battery involved.
Dual Charge Passthroughs - Some eGO and 510 batteries are actually a hybrid of the two - known as 'dual charge' batteries. They are a battery AND a passthrough combined and allow you to vape while the battery is being charged by a USB cable connected to the end of the battery. When you're ready to hit the road simply unplug the battery and go.
MODs and MOD Batteries - For the serious enthusiast we recommend a MOD. MODs typically house removable and often much larger batteries that are recharged using external chargers. MODs are often much bigger in diameter, weight and length, and thus usually more pricey as well. Mechanical MODs pass current directly to your tank or cartomizer while electrical MODs will have circuitry of some type often allowing you some measure of control over your vaping experience including voltage or wattage control, etc. Some of today's newer MODs like the BEC Pro from Smok even allow for Bluetooth connectivity with your Smartphone!