I'm gonna come at it a different way Bob -

AUW - 3lbs.

I'm estimating you need 50w/lb for cruising flight - therefore 150W

With 4s A=150/14.8 = 10 (or close enough) - so you need to draw 10A to cruise (or 10000mA). Therefore in 12 minutes you will consume about 2000mAh (12 mins is 1/5 of an hour and 2000 is 1/5 of 10,000).

Caveats:

I'm taking a guess at how much power you need to cruise - 50W per pound seems safe but ymmv.
This is all at cruising speed. If you go loud on the throttle you could probably divide your flight time by 2-4 (so somewhere between 2.5 - 5 minutes).

So maybe if you wanted some space to spare somewhere around 2500-3000mAh.