This is very important. Just last night I wasted $30 of batteries (2 authentic VTC4's). I'm lucky they didnt blow up.
always check on your batteries, and if they got hot, remove them from your mod!!
if they continue to get hotter/start to vent gas throw them into a tub of salt water so they may safely discharge.
Never put the batteries in your pocket either. Keys can short your battery! Use protective cases.
If you need a place to buy authentic Sony VTC4's (the safest battery I know) you can purchase them here:
http://www.illumn.com/18650-sony-us18650vtc4-2100mah-high-discharge-flat-top.html