Here are the ZenPad battery repair guides for the corresponding model. You will have to figure out which is yours.
ASUS ZenPad 3S 10: Follow this guide until you get to the battery part: [guide|93632]
ASUS ZenPad S 8.0 (Z580C): [guide|72939]
Asus ZenPad S8: Follow this guide until you get to the battery part: [guide|53249]
ASUS ZenPad Z8: Follow this guide to open it. Then you will have to figure out how to get the battery out.: [guide|120343]
I really hope this helps! Good luck.