Steve, I'd suggest carrying the two batteries in the rear panniers. I picked up 4 Ortlieb E-mate panniers for the expressed purpose of extra battery carrying capacity. These bags are perfect for the Bosch Powerpack, Yamaha and Shimano external batteries. Unlike other Ortliebs, these E-mates have a sleeve in which the battery slides into. That sleeve is attached to a hard plastic inner pannier liner that sees the battery weight taken up by the QL3 mounts to the rack. It will not bounce around in this bag with that sleeve setup.
Here is the Haibike on a run I did last summer trying to crack 100 miles, running from my home on the western side of the state of New Jersey, east to Mantoloking, New Jersey and the Atlantic Ocean waterfront. Inside both panniers were a Yamaha 500wh external battery. 3 batteries, running a fat ebike on all asphalt using High Power all the way east, then all the way west, back home. Photo 1 is close to home, early morning,parked next to some colorful Day Lillies. Photo 2 is in Jackson, New Jersey, about halfway east, about 20-25 miles in the trip. Break time. It was a long day, but an enjoyable ride all the way around, even in summer heat.
Heavy as a tank, yes, but very doable. To put the batteries in front is just going to make the steering feel heavy and slow, requiring a good long time to get acclimated to that kind of feel.