How do I change the battery on a withings connect?

So I want to change out the batteries on a used withings connect blood pressure cuff I bought on eBay. I can’t get them above 74%. It’s weird it’s one of the most popular wireless blood pressure monitors but there isn’t even a section. Nothing else on the internet either. There may be a reason for this. Things like”DON’T!! It will mess up the [insert reason here]” are acceptable