I bought the batteries from amazon. https://smile.amazon.com/dp/B0975WF9MD?psc=1&ref=ppx_yo2ov_dt_b_product_details
They're a bit different than the one inside the xm4 (3.7v vs 3.85). But they work fine. I've been using them for two weeks now.
I used the prying/opening tool from iFixit. https://smile.amazon.com/dp/B0762BVXDY?psc=1&ref=ppx_yo2ov_dt_b_product_details
Here's a vid of what it looks inside https://www.youtube.com/watch?v=-H7ST47BAyE&t=254s