The two most popular threadings are 510 and KR808D-1
I recommend manual batteries for all ecigs. Manuals are harder to damage or kill with juice leaks and make it easier to get a good drag/hit every time. Manuals also won't turn on accidentally in wind or vibration. Slim ecigs can use 2.5 to 3 ohm single coil atomizers and cartomizers. The lower ohms stuff is for fat models and mods, the high ohms are for high voltage mods. Re charge, 100mah is about 1 hour of moderate vaping at standard resistance.
510 has the most stuff, but a majority of that stuff is LR (low resistance) for all of the 450mah+ fat battery models and mods, not for slim 510 - however slim 510 still has a bit more variety of stuff then KR808D-1, but KR808D-1 is best at prefilled cartomizers. Slim 510 manuals are totally sealed on the threaded end and 180mah. They come with atomizer and cartridge but most use them as a 2-piece with blank cartomizers like Boge 3 ohm. One benefit of 510 threading is it has the most upgrade paths to larger models.
normal 510 is 180mah charge and 100mm long with a carto
the long mega xl 510 is 280mah and 128mm long with a carto
KR808D-1 is stronger (3.6-3.7v) and comes as a 2-piece with cartomizers. There are a number of vendors with good prefilled cartomizers for KR808D-1 as well as blanks. On a manual battery you can use a standard resistance DSE901 atomizer and drip tip for testing juices. Most use the standard/78mm size. Once downside is most KR808D-1 batteries have a fairly short safety cutoff of 5 seconds which may cut your drag short on a manual when you press the button in 1-2 seconds early so nice vapor is waiting when you start dragging. Just remember to only press in 1 second early or use V4L batteries which have a longer cutoff.
shorty/65mm battery - 180mah/220mah and about 100mm long with carto
standard/78mm battery - 280mah/ 320mah and about 120mm long with carto
(the longer charge numbers are for the rubberized models Bloog/Volt/G6)
if you want longer charge or the ability to use the hotter LR stuff, then you need to skip slim models and go right to the fat-battery models like EGo and Riva 510 or mods.
