Same Thing Happened With My Phone .Just 4 days before the warrenty was going to expire So asus replaced it for me. The screen Has yellowish Spot and a buldge on the back. Most Likely It Was water Damage in my Case Becz A day before My Phone got wet in rain.
Go on Ebay and buy an C11P1706 sure the don't last as long, one day of work. I did buy one with a kit of tools with so i open it and all, took about 10 min to complete. It is the same battery in M1 and M2, go on youtube for some information on "how to dissamble". Or if you want Asus to repair it for you it will probably be better to buy a new phone becuase of the cost. The new on the left and old bulky battery on the right.