Yes. The US Department of Transportation (DOT) regulations on passengers traveling with lithium batteries can be found at https://www.phmsa.dot.gov/safe-travel/batteries. Per the regulations, passengers may not carry spare lithium batteries in checked luggage unless they are within a portable electronic device. However, any number of spare lithium batteries are allowed in carry-on baggage if they do not individually exceed 8 grams (~100 Watt hours) of equivalent lithium content.
All Advanced Bionics lithium-ion rechargeable batteries (PowerCel™ Slim, PowerCel Plus and PSP/S-Series™ batteries) have equivalent lithium content weighing less than 1g each, which falls well within the 8g limit.
When traveling, protect the battery terminals by using the blue plastic PSP/S-Series battery cover or the Harmony PowerCel battery pouches. For Naída CI PowerCel batteries, use PowerCel plastic covers or a sealable plastic bag.