This is what I'm working on for mounting the detection devices at present. I'm using a lead acid battery because we will need something that doesn't run out in 12hrs e.g. so 7Ah, and we also will need 12v for the IR illumination anyway. They're not super-expensive - say £15-£20. Although I am a bit worried people might fancy to steal them! Note also, the sun hood with the solar panel on top. To prevent any glare during daytime usage.

I've come across an opto-coupled circuit that could be a way to isolate the IR illumination (12v) from the raspberry pi. http://www.amphioxus.org/content/raspberry-pi-security-camera

It's difficult to decide which IR illumination to use! We are going to need at least 60m range - maybe right up to 100m. We need to be careful how much power they will need! And also what people can purchase locally!  And the cost! I saw a fixed 140 LED light (in enclosure) 12v 18W 850nm supposedly 60m range outdoors (http://www.gowildlifewatching.co.uk/Wildlife%20watching%20IR%20Lights%20Night%20time%20filming%20CCTV%20.htm) but this was £100. Then I've got something like (https://www.amazon.co.uk/Illuminator-Angle-Range-12pcs-Lights/dp/B01MYNZ7TY) promising 100m range with 18W 12v 850nm at only £25. And for a 48 by 32  LED array that would be 180W!

So I think it's a case of building some arrays - getting plans out there for that - and also seeing how we get on with some of these IR illumination products you can buy.