While the question involves Git for Windows, this seems to be the top result even when searching for Visual Studio Tools For Git (extension in VS 2012, native support in VS 2013).
Using the solutions above as a guide I determined that Visual Studio Git Tools makes moving repos (or even entire directory structure for all repos) locally very easy.
1) Close Visual Studio.
2) Move the Repo folder(s) to new location.
3) Open Visual Studio. Open Team Explorer. Switch to "Connect" view (plug icon at top).
3a) If Repos still show old path, click Refresh to force an update.
4) Repos that were moved locally should no longer be showing in "Local Git Repositories".
5) Click Add (not new or clone) and select the repo folder to add.
In step 5 you really are just providing a search path and the search automatically includes all subfolders. If you have multiple repos organized under a single root (independent repos just having the same parent folder) then selecting the parent will include all repos found below that.
Example:
E:\Repos\RepoA
E:\Repos\RepoB
E:\Repos\RepoC
In Visual Studio Team Explorer [Add] > "E:\Repos\" > [Add] will return all three to the Local Repositories.