Your best bet (for ease of use and minimal frustration) is to get the G&P Crane Stock Batteries. You can get them in 8.4v, 9.6v and 10.8v configurations - but they come by default with DEANs connectors.
Therefore, you'll either need to convert your AEG to a DEANS connector (recommended), or convert the battery to a Tamiya mini connector. The swapping out of connectors either way, is well worth the hasstle free benefits of the G&P batteries.
The plastic sleeve they come with, holds the three groups of battery cells so they just slide into the crane stock without the wires getting caught on anything. VERY nice to have when you don't have time to fight with a battery when swapping it out or when you generally just don't need any extra aggravation in your life.
This same system also allows you to collapse the butt stock significantly further than the nun-chuck batteries do. Personally, I find the conventional "nun-chuck" battery set up nothing but a headache.
When I first got my CA M15A4 CQB SEAL, I fought with the nun-chuck batteries every time to get them into the Crane stock, and once in - the most the stock would collapse, was the furthest extension setting.
As time went on, I discovered that the G&P Crane Stock had more room in it lengthwise - particularly the side saddle compartments. However the CA Crane stock had wider diameter spaces for the batteries themselves, meaning they could take a larger cell (more mah for a Ni-Cd or Ni-Mh).
However, I swapped my CA Crane stock for the G&P one as I had plans to load two 11.1v 1200mah LiPo's into the side saddle compartments with the connectors at the rear, so a quick pop of the butt plate and I could quickly and easily switch batteries if needed. This only required minor modifications to the butt to access the connectors, and those modifications would only be visible when you took the butt plate off.
One of the other benefits of switching to the G&P Crane Stock, was that the buffer tube it comes with, has a groove cut out of the side to accommodate the connector wiring. This makes hooking up the battery and collapsing the stock a little easier than the stock CA one.
Lastly, the G&P batteries are also typically much cheaper than their nun-chuck style battery counterparts, though you will be limited in miliamps (2200mah).
However, if miliamps are that important to you, I would argue that for the cost of the batteries, and the ease with which they can be swapped out vs the nun-chuck style ones, you'd be better off getting two or more of the G&P batteries.
Anyhow, I'd definitely recommend the G&P crane stock batteries as the best Ni-Cd solution.
If you have any interest in putting a Li-Po into your gun (assuming you'll upgrade it to handle a Li-Po) then I'd suggest the Firefox 11.1v 1200mah (3pcs) Batteries. The 3 pieces per battery make it easier to slide the whole battery into one of the side saddles as opposed to the 1 piece batteries which are more rigid/less mailable.
Hope that helps Bud!