Nice rifle Daz
I can't really help you with your question but, on a full charge, it should last more than a full nights shooting - keep an eye on the battery meter on the screen.
I'd still have an Airwolf now if it wasn't for those electronics - they're right up there with the best that I've owned and, the 2 that I had were always faultless but, I just couldn't get over the thought of having electronics in a rifle.
Enjoy it mate