We carry batteries and chargers for that bike on our Currie® US Pro-Drive Electric Bicycle Parts page.
If you want to add a second battery pack on a rear rack that is possible. Maybe a BAT-2410PK Battery Pack and CNX-2PX2 or CNX-2PX4 Power Connector could be could be strapped onto a rear rack to serve as a second battery pack.
You are welcome. One more thing I just thought of is that we have a box of brand new battery packs for the Currie US Pro Drive electric bicycles. These new battery packs include the plastic case with built-in handle, power switch, charger port, etc, and the metal key to install and remove them from the bike's frame. The batteries in these battery packs are very old so we will replace them with brand new fresh batteries upon their sale.
Just wanted to let you know about this second OEM battery pack option in case it is something that you may be interested in.