Why won't my tablet charge completely

hdjuback , Try to charge your device again, making sure the charger is plugged snugly in charge port. Verify charger is in deed working( try it in another tablet if able), charge port could be loose/damaged, battery connection or charge port connection may need cleaned and reseated, battery could be defective.

If still under warranty return device for repair/replacement/refund. If not you may want to open the device and check the connections(charge port/battery) and clean them with Qtip/soft bristle tooth brush dampened with 90% isopropyl alcohol and reassemble and try. Below are links to a couple guides to show how to open device to access/change charge port/battery. Some replacement parts are available for the Galaxy Tabs at the iFixit store, last link if needed. Good luck.

I hope this helped you out, if so let me know by pressing the helpful button.

Galaxy Tab S 10.5 Charge port Replacement

Galaxy Tab S 10.5 Battery Replacement

Samsung Galaxy Tab Parts