I recommend a few 9v batteries in parallel to increase your mah
Yes. and Yes.
Check price for same at pololu.com also.
Duration will depend on how much else you have connected.Generally, 30mA or so for the Arduino.With NTX2 radio transmitter and a GPS receiver? Not enough info provided. non-rechargeabe AA battery is good for 2200-2500mA or so.Individual Li Ion, like 18650, good for 2200mA at 3.7V (check the tenergy website to make sure).Do some ground testing first; batteries become less efficient at temperature extremes.
Well 2200mAH x 1.2V = 2640mAVH, or 2640mWattHours. Divide by 5Vx30mA, 150mW, yields 17.6HoursThere's a switching efficiency factor in there too, so probably somewhat less. 90% maybe? so 15.8Hours.
Are you thinking NiCad, is that where the 1.2V is coming from?