Giant doesn't seem to have the 2021 Revolt posted yet, but the Road-E has been up for a bit. AFAICT, the frame is the same, but they list it as having a 500whr battery. Checking their parts store, they do indeed list a 500whr battery thats compatible with the 2020 line:
EnergyPak is the fuel for your E-bike that allows you to explore your world without worrying about running out of power.Upgrade for the follow E-Bike bike model...
www.giant-bicycles.com
(strangely no 2021 bikes are listed as compatible, which I assume is an oversight, or maybe just not listing them until the entire 2021 lineup has been posted).
Wondering if the size is exactly the same or if they bulged it out to the side to fit more cells. Only reason I'm not ordering one is my wife has basically taken over my Revolt and I'll probably pickup a 2021 early next year.