I had similar problem. It is an older ellipsis. Not even sure if it was a 7. The battery symbol came on when plugged in but stayed at 0% charged. I tried holding power button down, holding it down with volume button down. Nothing worked. Then I tried disconnected battery for 1 minute. Reconnecting and plugged in charger. SOLVED! Battery starting charging right away.
Note: It was a lot more difficult to take the back cover off than YOUTUBE videos show. Very hard snaps. I had to take a very thin blade metal trowel to get it started near a corner. Then used a plastic stiff wedge type tool to unsnap the cleats one at a time. Once the cover was off and battery was exposed, it was not obvious how it disconnected because there were no obvious ribbon plugs connected to it. I figured out that at the top end was a tab that was attached to battery and was screwed down against the mother board. That was the battery connection..... a simple contact type connection held in place by the two very small screws. Hope this helps those with similar issues that have tried everything else.