This is the one I bought, but it’s swelling again.
This is for the 910 model but it works just fine until it swells again.
New LI3823T43P3H715345 Battery For ZTE MF910 MF910S MF910L 3.8V 2300mAh 8.8Wh
i actually am getting a different hotspot entirely and will likely try to sell or throw this one out. The service I have isn’t great and this hotspot kills the batteries and also is very inconsistent. Sometimes I have to reboot it just to have signal (in the same location)