Search online for C12P1601 battery for suppliers of the battery that suit you best.
Usually the battery model number is printed on the battery if you wish to verify that it is the correct one.
A quick search online shows that it is not cheap
I looked for an Asus Z500M battery and found this supplier.
Then I clicked on the image of the battery in the link to enlarge it and on the battery you can see the battery model number i.e. C12P1601 and the Asus part number for the battery.
Then I searched for the battery model number
(click on image)
Alternatively you can also search for the Asus part number 0B200-02110000 (examples only)
The same battery can be used in different devices/models. It happens frequently with devices/models made by the same manufacturer