I have a pair of 3000 mAh 35C Wild Scorpions that weigh in at 12.5 oz each c/w connector.  That was about as light as I could find at the time I bought them but Revolectrix now has similar batteries at under 12 oz., although that's without connectors.  I've used them for only about half a dozen flights so I can't speak to longevity but I find that they're within 2 or 3 mA of each other when I recharge so I guess that shows some consistency of quality.

Where are you sourcing them?  The place where I bought mine seems to have disappeared.

I found them in a couple of places. I was interested because they were selling a 5s, 25c, 2800mah battery. I could use the extra 100mah.