I have used the TP-Link M7650 as a home router for almost 2 years in the countryside (because there was no other affordable way to use fluid internet). It gave me 3-5 Mbit/sec, with severe limitations and weather conditions. Eventually, it became defective because it was apparently permanently connected to the mains.

TP-Link was very accommodating and offered me a replacement after almost 2 years - I decided on the replacement, but no longer the TP-Link M7650, but the Archer MR600. Since then I have had a more stable internet than ever...

I would only use the TP-Link M7650 for holidays and no longer as a home router. I hope I was able to help you with this, vG Stephan

No, unfortunately there is no connection for an external antenna.
I don't know of any mobile modem with a powerbank and external connection.