Battery

This is a standard '510' battery.  This particular one has a blue LED light at one end, and a female connection at the other, to accommodate either a '510' cartomiser, or a '510' atomiser and tank/cartridge combo. The other most common kind of battery you will encounter is an '808' - this usually has a male connection, to accommodate 808 atomisers or cartomisers, which usually have a female connection.  There is no real difference between 510's and 808's apart from the male/female connection configurations.  The 510 battery is usually slimmer on smaller e-cigs, but with larger e-cigs, 510's and 808's are pretty much the same size.

Many bigger batteries have 510 fittings, including, for example, this one:

Although this looks very different to the first battery, it has exactly the same '510 female' configuration and can accommodate exactly the same atomisers and cartomisers.   It is much bigger, (about twice the length and diameter) but nearly 10 times more powerful, meaning that it will last 10 times longer between re-charges.  So, with the first battery, you need a PCC to keep your batteries charged, on-the-go.  The second battery (at 900 MaH) will keep most people going all day.  Sometimes, though, very big batteries wear out very quickly , and they are relatively expensive to replace.

Recommendation:  There is no meaningful difference between 510 and 808 batteries.  

Automatic and Manual Batteries

Another difference between the two batteries pictured, is that the smaller white battery is automatic, meaning that, after you plug it into your cartomiser, it will activate simply upon you drawing on the e-cig, as you would a normal cigarette.  The second battery is manual, meaning that you have to press the button to activate the battery, as you drag on the cigarette.  What’s the point of that, I hear you ask?! 

Well, some automatic batteries have, in the past, been a bit sensitive, although those that were have now been improved and this is no longer a problem.  What I mean by this is that these batteries were inclined to activate at times other than when you draw on the cigarette – like if you were carrying it around loose in your pocket, or if you knocked it.  This shortened battery life, and decreased the time between charges.  Now, a manual battery might be less likely to self-activate, but it is still possible unless, like the larger battery pictured, it has a locking function.  Pressing the battery 5 times quickly locks the battery and so no amount of abuse is going to cause the battery to self-activate.   Having said all of this, it is very hard these days to get an automatic battery to activate, and pretty hard to knock or abuse a manual battery causing it to activate.  So, manual batteries are uneccesary, and manual batteries with locking function doubly so - this is a good example of people making things more complicated than they need to be.

Recommendation:  Go for automatic batteries.  Firstly it will not be natural for you to have to press a button to get your nicotine – that’s just awkward!  Secondly, automatic batteries just do not self-activate any more.