IceFireSoul said:
Aha, we are on the spot here!
Why 45C better than 20C?
Does 20C run down quicker?
What's the truth?
If they are at full or almost full capacity, the 45C & 20C pack may not make much difference. This is because the 4 motors at "hovering" may take about 18 amp for stock Phantom; 20 - 25 amp with extra gear. Both 45C and 20C can put out 99 amp & 44 amp respectively which is more than enough for hovering.
Now let assume, we are half way through the pack, so both packs now have 1100 mAh in stead of 2200 mAh; therefore they can now only supply 49.5 and 22 amp. At this point if your Phantom carries the video gear and needs 20 - 25 amp just to hover, then the 20C pack is about at its maximum capability and if you open up the throttle to climb, you may get the RED warning low voltage and your Phantom may not climb as fast as you want. On the other hand, the 45C pack can still deliver plenty of power for the same situation.
If the scenario goes on further, the 20C pack will be ready to quit depending on the AUW but the 45C one will be able to give you more flight time. Then you will ask, okay why not go for the much higher C rate like 65-130C pack. The answer is the price, the weight and the overkill factor where you may get additional 30 seconds for $35 more per pack, plus longer charge time.
Again depend on the flying weight and other factors:
http://www.hobbyking.com/hobbyking/stor ... ecker.html
I use the gadget above to check my pack after the flight and I set the low voltage to a point that the pack has about 20% capacity left.
People fly their Phantom with different weight, props and etc (not to mention at different attitude), so I think the best bet is to use the device above as the decision factor rather go by how long it flies.
Moreover when the weather changes whether it'll be temperature, wind or humidity you may need to adjust your setting accordingly, so again this gadget will come in handy.