User Manual Samsung SM-T500NZSEXAR Galaxy Tab A7, 64gb

While the Samsung Galaxy A7 Tab 2020 does have Android OS 10 and Bluetooth 5.0, I would recommend contacting the hearing Aid company or Samsung directly to confirm compatibility.
From looking at the ReSound website's device compatibility list, the Galaxy A7 Tab is not compatible. The Galaxy S-series and Note-series both seem to be on their compatibility list.
This Q&A forum is posted by consumers and is NOT maintained NOR support by Samsung or Amazon directly.

According to the User Manual of the Samsung Galaxy A7 Tab, the battery can be changed at a Samsung Service Center.
So, it could be replaced by someone with enough technical skill and tools.

The Samsung Galaxy A7 Tab supports up to 1TB via the microSD slot. I've got the Samsung 256GB microSDXC for $24.99 (Amazon item ID B0887P21Z2)
Amazon also have smaller size microSD sizes available for the Black Friday Sale. Please note that the A7 Tab does not support installing Apps onto the external microSD drive. It is only for files.

It's not critical at all since the 32GB or 64GB is storage size, there isn't much of a difference since it supports external microsd storage up to 1TB. Unless you install an insane amount of Apps, it would be cheaper to get a microSD flash instead of paying $30 or $50 more for the the additional 32GB storage upgrade to 64GB. A Samsung 32GB microSD $7.50 and a 128GB microSD is $19.99 as of 2020/11-14.