iPad mini stuck at 0% remaining, always rebooting.

Did you get the ipad fixed at a repair place? if so, i would recommend taking it back to them or another shop to have them check it out.

generally when I-pads do this, there is a slight chance it could be a battery issue, so it'd be worth having a shop connect one to see, but most likely its a motherboard issue with the power delivery IC chips. Most shops will have a tri-star tester that can read if there's a problem with any of those main components, but it may read fine and there still be a problem somewhere else on the motherboard.

often these chips will hit and end of life or burn out after so long depending on conditional things like exposure and use, but sometimes you can treat the device fine and it will just ultimately give out. Liquid damage could also be a cause. But its hard to give any definitive's off of what you're describing without looking at it and trying a few things to narrow it down.