permission for network users

I have a laptop (A) which connects to a PC (B) via LAN. B is a backup computer. I have batch files that copy files from A to B all the time.

Last week, I reinstalled Windows 10 built 1903 on B as a clean installation. So, everything on B, Windows, apps, settings, etc., are all gone except the files. Now, the batch files don't work because I don't have permission to modify files on B. I now need to grant permission on B to users on A.

I'm the only person who uses these two computers. No other people do. So, my situation is relatively simple. There are two administrator accounts on each computer, the default Administrator account and another administrator account. They had had the same userid and password on both computers until one day I unwittingly changed the default Administrator on A to a Microsoft account. The other account stays the same on both computer.

If my memory serves me correctly, on all drives on B, I had in the sharing permission administrator/administrators and they had full control. In security, the administrators also had full control. Such settings don't work now. Some articles on this site say I need to grant, on sharing permission, full control to everyone. Is that safe (can't remember if that's how I did it)? I know I'm the only user but just in case there are hackers, intruders, etc. I want to stay on the safe side.

Go through and double check those batch files. You arr welcome to post them.

I don't think it's the batch files that are the culprit. I can open files on B, I can edit files on B, but I cannot save the edited files on B. Error message says I don't have the permission to save files. I cannot rename files either.

The batch files had been working for at least 3 years until I re-installed Windows on B. I really don't think the batch files are the culprit.