An rc battery probably would be suited more to a led setup, hid's have a huge draw so you'd probably need the biggest ones available.
I just thought I'd share a cheap, easy, and tidy alternative to mounting a battery in a purpose designed box
T6's are for stock bikes, if you port they won't work as well as the t5.
CPI would be the best bet as they'll keep giving if you decide to do some more modding to the engine.
I second johns comments, I've had a dc setup stator and regulator in my bike for around 7-8 months. It's handling huge wattage and doesn't let the bulbs drop one volt when I demand more power from it.
This really is a high quality piece of kit, Evan is putting himself out there to make you guys happy offering various stator types. What more can you ask for.
I found some old pics laying around, this was when I first mounted it up (I later replaced the brackets with some thicker ones)
Here's the part number for the 450 ktm battery tray, it worked out about $12 for the tray and rubber battery holder from a ktm dealer. It's great value for the money.
I haven't had no faults to date, the stator powers up my 55w per side street bike lights as well as a led rear without problems.
As for fitting a battery with an airbox it can be done. I ran a ktm 450 battery box at the coolant tank location. I'm running pods now so I'm going to move it further forward.
I've also seen one mounted behind the bumper, I prefered it up higher though.