Ra is waterproof but the BatPak is not. Ra is rated IPX7 which means it can be submerged in water up to one meter for 30 minutes. The USB ports on the BatPaks are vulnerable to water. If enough water gets into the ports then the BatPak will shut off.
Ra is exposed to the elements so being waterproof is a good thing. Typically the BatPak is stowed in a pocket, pouch or pack and somewhat protected from water exposure. If you stow the BatPak with the ports pointed sideways or downward, it will minimize the potential for water to drain into it. If your BatPak fills with water to the point it shuts off, drains the water and fully dries out the Batak. Then you can turn it back on. However, they recommend you avoid that scenario by protecting your BatPak from water.