i fly a 4.8v 600maH battery on a 5 servo FF. and have no worries getting 4or 5 flights of up to 10min ,
i think but not to sure on this, correct me any one if im wrong.
at 50mah it will take 20 hours to charge 1000mah pack, the 120mah charger will do it in 8.5 to 9 hours.
there is a way to calculate the mah used during flight but i dunno it, but someone will be able to help u

Battery Clinic:
Know what your system consumes in the way of energy per minute of flight. This can be determined by first charging a pack and then discharging it on a cycler to determine how much capacity it has - fully charged. Then recharge and go fly. Record your system on time and immediately discharge the pack when you return home. This will tell you how much capacity you have left. Lets say you fly for 40 minutes and when you discharge the pack you get 390 mAh. From your initial discharge from a fully charge pack you got 585 mAh. This would mean that you discharged 195 mAh in the 40 minutes you flew or about 5 Ah/min. From this you would know that your pack is good for 116 minutes of flight time under the actual flight loads. Now we don't want to take it this close so give yourself (and your plane) some margin of saftey -25%. So this would set your SAFE flight time to 75% of 116minutes or 1 hour 27 minutes. This should be done for each plane. Also it should be done for your transmitter at least once just to acurately characterize its "flight time". The system usage will vary, depending on your flying style, size of the plane and number of servos used.