Fix bugs in add_energy_storage_database

[millingermarkus]

Closes # (if applicable).

Changes proposed in this Pull Request

The previous version did not run through the add_energy_storage_database anymore, these changes enable it to run through.

Checklist

• [N/A] Code changes are sufficiently documented; i.e. new functions contain docstrings and further explanations may be given in doc.
• [N/A] Data source for new technologies is clearly stated.
• [N/A] Newly introduced dependencies are added to environment.yaml (if applicable).
• [N/A] A note for the release notes doc/release_notes.rst of the upcoming release is included.
• I consent to the release of this PR's code under the GPLv3 license.