How to run iPad without battery?

iPad is designed to run with a battery, thus there’s no really easy solution for your need. Not sure if the system requires also a battery presence acknowledgement or it’s sufficient a component bridging, but unless you’re able to microsolder and have the necessary tools is not a very handy solution. If you have to find and pay someone doing the job you’d end up paying multiple batteries cost to get the job done. All in all I believe a battery replacement is the easiest and cheapest solution.