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