So I purchased a pre-built USB boost circuit from Jaycar Electronics, and soldered a 3 volt lithium battery onto the terminals. Then when I went to plug in the iPad it didn’t recognise it as a charger, instead as a USB accessory. I waited a couple of hours to see if it did charge, it still didn’t. I tried plugging into something other than the iPad and was successful charging other devices that weren’t apple devices. I’m not exactly sure what is wrong with it, but if you could help it would be great.