Power bank for Macbook Pro?

Does anyone know of a power bank for my MacBook Pro (mid 2014)

that would connect directly to the MagSafe2 power plug?

I would be content with a power bank that could extend my battery by a couple hours.

I already did a lot of research, to no avail.

I found only very few power banks suitable for MacBook Pro, most of them were made for the Macbook Air.

And I found none that would directly connect to the MagSafe2 plug.

I will appreciate all kinds of hints and suggestions.

Best regards,

Gabriel.