Could someone explain the theory of battery choosing please

[Yam]

Hi all, Newb with an F450 here
This is the kit that I have at the mo:
4x 15 Amp E300 Speed controllers.
4x E300 2212 920kva Motors
6x E300 9" Self tightening props (cw/ccw)

I am currently using (after being reccomended by someone) the Turnigy 5000mAh 4S 25C
http://www.hobbyking.co.uk/hobbyking/store/__26740__Turnigy_5000mAh_4S_25C_Lipo_Pack_UK_Warehouse_.html

It flies fine, as far as I can tell, but how did they come up with that battery choice?
I could do with another battery or two, but would like to know how to go about choosing one rather than having to ask.

Any advice appreciated as always

[Revs]

Hi Yam. The E300 system is rated at 600g/axis thrust with a recommended hover weight of 300g/axis, so you';re gonna have to careful with weight. With a target weight of 1200g you';ll be best off with a 2200-3000 mAh 3s.

As you have 4 ESCs at 15A you need a battery that will deliver 60A. The C rating is calculated as follows...

With a 2200mAh (or 2.2Ah) battery..
60 / 2.2 = 27c (30c is the nearest)

With a 3000mAh (or 3.0Ah) battery..
60 / 3.0 = 20c

This is a minimum, it';s always good to go a bit over for better performance. I';d try a 2200 3s first. It doesn';t sound very big but you';ll get 10 mins out of it with a 1.2kg quad easily.

[Yam]

Cheers for that Paul, just what I was looking for.

I havent weighed my quad inc the battery but the batt I have is marked as 552g, so with something like this
http://www.hobbyking.co.uk/hobbyking/store/__73744__ZIPPY_Compact_3300mAh_3s_40c_Lipo_Pack_UK_Warehouse_.html
which comes in at 277g I should see a quicker, more responsive flight, albeit a shorter time?

[Revs]

Yes, but not that much shorter. With a bigger battery, more energy goes in to lifting it, so it negates the advantage having more capacity to an extent. Also as you say it makes it a little more sluggish.