iPhone not turning on.

My Niece handed me her iphone to fix, but I can't. When turning on, the apple logo comes up for a few seconds and then the screen goes black again. I've tried forcing a restart by pressing the up/down buttons in turn and then pressing the on button, no luck. I connected via USB to my imac and the phone shows up with two options - update software and Reset. I did both but still have the same problem. I'm begining to think it could be the battery, her phone is a 10XR. Any suggestions appreciated.