I use a 510 and vape fairly heavily.  The regular batt for me last 1.5 - 2 hours.  The mega 510 batts (got mine from Totally Wicked) last much longer.  I got about 5 hours out of mine last night.  
Get a passthrough for use through a USB, no batt, while you are on a computer.  Also get a PCC charging case.  It will recharge a regular 510 batt in less time that it will take to use one up, and it will charge up to 4 batts before it itself needs to be recharged (its a case with a its own battery that charges 510 batts).  PTs and PCCs both cost about $20, depending on where you get them, and are sometimes much lower.  
happy vaping!
Kurt