3.8v batteries designate HV (high voltage) which charge up to 4.35v. Where normal lipos are 3.7(4.20 fully charged)

You'll want 1s 450mAh HV batteries same as the original because larger batteries will greatly affect the performance from the added weight. Emax/URUAV/GNB/RDQ are all great battery brands for the Tinyhawk.

You can geta 5pack of URUAV 450mah batteries for $21 w/free shipping on eBay from US sellers. Racedayquads.com also have a 5pack of their own batteries for $21 + shipping.

Here is a 6pack on Amazon https://www.amazon.com/Batteries-Compatible-Quadcopter-TinyHawk-HAPPYMODEL/dp/B07X1T44QT/