I found that on some Debian installations, ssh-add would not remember the passwords post the life of an ssh shell. If you need to get it to remember it permanently, you need to add the following to your ~/.ssh/config file (create the file if it does not exist already):

#cat ~/.ssh/config
IdentityFile ~/.ssh/id_rsa_mykey

Provide the path of your private key.
This key will be remembered for ssh authentication and also for a git push like in Bitbucket or Github. I’m not sure why the key gets remembered in some Debian installations.