Carver, most ignitions we use for gassers require a 4.8 volt battery set up or 6 volt with a regulator.
If you have set up your system with a manual on/off switch with a built in charging jack then when you plug in the charger it will automatically
isolate the ignition side of things so only the battery is getting any charge.
Charge the battery at a rate of 1C being 1/10 of the batteries capacity. ie; 1800Mah pack charge at 1.8amps for 16 or so hours for full charge.
If you have a fast charger then you can top up at the field. Just read instructions.
Have a look over at the giant scale forum and have a good read Mate. A wealth of knowledge there.

AA or sub C size does not matter apart from size and weight restrictions for you model. I use a 2500 NicMH AA pack in my 27% Extra/ZDZ80 twin and get 4 flights and then charge all batteries up.

HTH

Brad