Hi there,
So, I think you misunderstood the WiKi “Battery Section”
, a LiPo battery is not a standalone lithium battery, but a type of lithium-ion battery
from the WiKi …
If you want to connect the battery for XIAO, we recommend you to purchase qualified rechargeable 3.7V lithium battery
Lithium battery vs. Li-Po, YMMV 
HTH
GL 
PJ 
FYI , charge current is 51ma.
To find the charging time (T) you can use the formula that relates capacity and current
T=C/I
𝑇=2000mAh @51mA
T≈39.22 hourscap T is approximately equal to 39.22 hours
𝑇≈39.22 hours
That’s a long time to charge… 
I would re-evaluate your plan go for some deep sleep on a smaller battery. What is the App?