iPad Air 1st Gen not actively charging despite gaining battery percentage
My 1st Gen iPad Air has been dead in a cupboard for a year or so. Plugged it in last night, did a factory reset, iOS is up to date, charging port is free of debris, and I am using a new Apple cable and block. The iPad is gaining battery percentage, but is not showing that it is actively charging. It's gone from 12% to 25% in about 24 hours. I have tried other outlets, and I seem to be getting the same result.
Could this be a bad battery or a bad charging port?
[Re-Titled by Moderator]
Original Title: 1st Gen iPad Air