I don't think buying a Racktime-compatible panniers is necessary. Ortlieb with their QL2.1 universal mounting system are unbeatable, and you'll discover that when you own more than a single e-bike.
I have eventually standardised on Ortlieb Bike-Packer Classic panniers with Ortlieb Commuter Inserts. As I've already said, the QL2.1 is universal and easy. Just lower the hooks of the pannier onto the rack, then fasten the bottom of the bag with the hook and you're there. Want to take the pannier off the rack? Just lift it with one hand.
The panniers I mention are strong and truly water-proof (tested out!). The Bike-Packer Classic easily holds the large Giant EnergyPak battery (46 cm or 18" long) and the Vado/Como battery fits even easier. The Commuter Inserts convert the "baggy" pannier into organised and reinforced transport container.
I have never understood all the hype around the Racktime system.
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So easy is to mount the pannier on and even easier to remove it from the rack.
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Yes, my brother has applied some tape to prevent scratching.
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So spacious the Ortlieb Bike-Packer is: The Specialized and Giant batteries plus a water bottle. The Ortlieb Commuter Inserts protect the bottom of the pannier and help organise space. Not that I would recommend carrying as many as two batteries in a single pannier, for the balance issues. Just showing how big the pannier is. I can guarantee I could use the inner nylon sleeve to secure the pannier contents and give more rain protection to it. The pannier is eventually enclosed with a waterproof cover flap. A carrying strap completes the system (I'm taking the strap off for longer rides, so it cannot get in conflict with the spokes).