Batteries that are integrated into the downtube are increasingly being used to keep an eBike looking stealthy so they blend in better. Like downtube batteries, this battery's location advantages include better handing because the bike will handle most naturally the closer the battery is to the cranks where the pedals are. This location can also be used on step through designs - allowing easier entry at the same time having ideal weight distribution.
A common problem with integrated batteries is that they can pop out if not properly clicked into the frame mount. Replacements can cost $800+ so seeing your battery tumbling down the road can be a heartbreaker. Make sure to click it!