From my understanding it varies from airline to airline.
I’m looking at the Air Canada page that has details for example which can be found here.
But I’m not sure certain what it means.
Can I have a portable power bank that’s 160W? If I bring that could I also bring on a laptop and a Steam Deck?
It seems like you can bring 15 devices theoretically.
I’ve been looking into this as an electric wheelchair traveller, there are guidelines, but it’s also up to the airline. I’d talk to them first and see what they say.
https://www.faa.gov/hazmat/packsafe/wheelchairs-mobility-devices
"Lithium ion battery size is limited to 300 watt hours (Wh). One spare battery not exceeding 300 Wh or two spare batteries not exceeding 160 Wh each may be carried in carry-on baggage.
Lithium ion batteries must be removed from this type of mobility device and battery terminals protected from short circuit. The battery must be protected from damage (e.g. by placing each battery in a protective pouch). The lithium ion batteries must be carried in carry-on baggage only. The passenger must advise the airline of the battery location. The airline must notify the Pilot-in-command of the battery location in the cabin.
For complete passenger instructions contact your airline or the mobility device manufacturer on how to transport your battery as a passenger. Advance arrangements and extra check-in time may be necessary.
Individual airlines may have more restrictive rules regarding the acceptance of any dangerous goods, including lithium batteries that power mobility aids."