Unexpected shutdown when using battery on Macbook Air

My Macbook Air 13 inch (early 2015) unexpectedly shuts down when off the power adapter for an hour or so. If it was fully charged it will still just shut off with no warning after about an hour and I've never seen it get below 40%. It won't restart until I plug it in. It says "battery service recommended." It only has 218 cycles so it shouldn't be doing this. Must I go into an Apple store?? Or can I just buy a replacement battery and DIY?