Yes lithium battery power chairs are allowed on commercial aircraft. If the battery is in a protective housing built into the wheelchair it can remain in the wheelchair. If it's removable the traveler must carry it in their carry-on luggage. Lithium-ion battery size is limited to 300 watt-hours (V * Ah = Wh) (max 12.5ah 24v battery). One spare battery not exceeding 300 Wh or two spare batteries not exceeding 160 Wh each (max 6.6Ah 24v) may be carried in carry-on baggage. So you can bring along up to three 24v 6Ah Lithium batteries, or two 24 12ah Lithium batteries. Federal Aviation Administration (FAA) official instructions for Wheelchairs and Mobility Devices with Lithium Ion Batteries