Starter kit batteries are usually the round style popularized as eGo or EVOD style. These are slightly larger than the Cig-Alikes (the ones that look like traditional cigarettes) but provide significantly longer vaping times between charges.
The easiest way to tell the difference between an eGo and EVOD battery is by the firing button ... at the right, that is the round button in the silver top portion. On the eGo style batteries, the round button sticks out slightly.
The EVOD style is round as well, but is form fitted in the battery tube and flush with the side of the tube.
By the way ... these buttons are also called firing buttons or actuator buttons.
Other differences you might notice are all cosmetic: the top connector area on the EVOD is not quite as tall (less chrome or silver) which helps make the Clearomizer appear more fitted as a unit, particularly if it is the same color as the battery tube.
Other than that, there isn't much difference between eGo and EVOD. These types of batteries are rated by mAh or "milli-amp hours". They start from 350 mAh, 400 mAh, 450 mAh, 650 mAh, 900 mAh, 1000 mAh, and 1100 mAh. Recently some new models extend that to 1500 mAh, 1600 mAh and one pushes the limit to 2600 mAh.
Milli-amp hours (mAh) in layman terms is a way for your to tell roughly how long the battery will last. As a general rule of thumb, someone who used to smoke one pack a day and continutes to vape along the same usage will get about 1 hour of vaping for each mAh before the battery needs recharging. That means that a 650 mAh battery will last approximately 6.5 hours.
So far, these are all constant voltage (3.7 volts). There are also eGo and EVOD style batteries that are called spinners or twisters. They are both the same, they feature variable voltage that can range from 3.2 volts to 4.8 volts (and some are a range in between that). To provide this feature, the manufacturers add circuitry in the battery tube so that your battery outputs a consistently higher (or lower) voltage to the atomizer. If you look at the picture just immediately below and to the right, you should see the bottom of the battery has a silver ring with a red line on it. The numbering system that red line points to is the range of voltage this particular spinner ranges (3.2 to 4.8 volts). That ring and the action of "spinning" or "twisting" is why they are named like that.
So, why would you want to do this? Well, a constant voltage battery will output whatever voltage is available from the battery directly to the atomizer. Some vaping liquids and coils will do well at this voltage, while other vaping liquids might need a bit more of a voltage "kick" to deliver more flavor or more vapor. With variable voltage, you can also get the same effects as a lower resistance coil by increasing the voltage, or higher resistance coil by lowering the voltage. Most users would consider variable voltage to be an enhancement over and above constant voltage systems.
Your choice in batteries is not limited to the black and silvers as shown in pictures so far. These style batteries are available in a rainbow of colors (and even rainbow is a choice). Black, white, pink, gold, purple, blue, red ... you name it, the color is likely available – in constant and variable voltage models.
The variable voltage batteries discussed so far are "infinite" style (within the specified range). There is also another type of variable voltage battery that has fixed increments. These change the voltage by multiple presses of the firing buttons.
eGo and EVOD style batteries remain the most popular systems in personal vaporizers and advanced personal vaporizers. An excellent strategy is to select two or three of these batteries to last you an entire day. For example, if you get three 650 mAh batteries, you have approximately 16 to 18 1/2 hours of vaping. One should last close to a full working day, perhaps needing a second to complete the day and drive to work/home. Once home, recharge the spent one.
Both eGo and EVOD style batteries provide dual connector types: 510 connector and eGo style connector. That's the widest compability available for almost any style of Clearomizers, Cartomizer or Rebuildable Atomizer. If you can find these with a floating center pin, that's a bonus. A floating center pin is the positive connection post. There are some that are fixed and get pushed down a little bit by some clearomziers ... try the next clearomizer that doesn't have as long a connector pin and there is no connection. A floating pin connector solves this issue.
eGo and EVOD style batteries have internal lithium-ion batteries. These are good for 350 to 500 charge cycles before they will no longer hold a charge. That's about one full year of vaping before you need to replace these.
And, one final note. Get a known brand. We've been contracted by several retailers looking at various manufacturers to source their eGo and EVOD style batteries. Some of the batteries we've seen make us cringe at the thought someone is using these. The tubes are either painted brass or thin brushed stainless steel. The battery should have a negative lead that is soldered to the tube and soldered to the connector top. There should also be a positive lead that is soldered to the center connector pin. We've seen these batteries with no negative lead – they solely rely on the bottom of the battery providing the negative contact to the bottom of the battery tube and the battery tube providing the continuity to the negative portion of the connector. Nice way to get a little buzz ...