Venue 8 Pro not charging?

I have not used this tablet a lot for the first couple of months I had it, then it was not used for 4 months I enjoyed it but mainly wanted it for travel. I used it for month while traveling in October it worked fine and put it up since then I got it out and put it on charge the same cord and charger that came with it and has worked in past. The white light will come on but after say ten mins goes off and the tablet is warm on the back, it has not charged if I try to reset by holding the buttons down I only get a couple flashes of Amber light. And when I plug the charger in no lights come on. Then if I wait like an hour and plug charger back in the white light comes on and again only stays on 10 mins or so and warms up the back. The warranty period is over as of 4-2, any thoughts, bad battery due to letting sit and battery going dead for so long? Tried three different cords but only have the one dell charger.