I dunno, Trinity, battery packaging is the most difficult problem for E-bikes. The Neo Volt Sport (like yours and mine) has a fat banana shaped battery with very vulnerable contacts underneath at the back.
Us your existing battery to check if this works:
Protect the top of the spare battery against scratches and minor mechanical damage with rubberised fabric or something like that.
On the journey, carry your spare battery underneath the existing battery and fix it in place with nylon electrical ties (Zipties) When you need to swap batteries, cut off the zipties and discard. Use new zipties to secure the second battery for the homeward journey.
My experience with the Neo Volt Sport suggests that one battery will give you 72 km (45 miles). The tender parts of my body couldn't survive a longer journey on an unsprung bike. You could ask a friend to bring you a spare battery by car when the first one is depleted. Or you could carry your charger and visit friends for a few hours every 72 km.
Crazy Lenny may have a better solution, if he still visits the forum