I found a guide on how to do this repair and I also have found the right battery for this Phone.
However this battery is not sold by iFixit so you will buy this at your own risk![br]
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[https://www.youtube.com/watch?v=d0fiH5Sv1cM|Tutorial Video][br]
[https://www.ebay.com/itm/NEW-Battery-For-ZTE-GRAND-X-MAX-2-Z988-ZMAX-PRO-Z981-Li3934T44P8h876744-3400mAh/371988540912?hash=item569c3eadf0:g:c4MAAOSw9H5bMaE3:sc:USPSFirstClass!80504!US!-1|Replacement Battery]