Hello Olinik,
And where can you find this kind of external battery?

It is possible but not practical, the charging cable runs perpendicular to the back of the GPS. You would need a large hand to hold it. I don't see how it could be fixed with an external battery.

Hello,
I used it as recently as the Easter weekend to walk around Beaune and Dijon without any problems. The capacity of its internal battery was sufficient. But I can't answer the question if it is possible to connect it to an external battery, I think not.
Have a nice day