It honestly depends on a few factors. Mostly… what games are you planning to play? There’s stuff that can last for 5-8 hours with the Deck battery alone. Here’s a good bit of information: mentions both a maximum of 100wh on power banks and how to calculate wh from volts and ah (V * Ah). So assuming the usual 3.6v power bank the maximum you can carry is a 27000mAh one.
The usual warnings apply: check in advance with your airline, rules and regulations vary around the world and so on.
I wanted to shit on Lenovo because when I bought my laptop last year they had no Linux laptops (anymore) and specifically an article on how to install Linux links to one that just explains what an OS is… but I actually double checked before posting and it’s looking promising! There’s a list of “best laptops for Linux” including the Mr Moneybags version of mine, and a bunch of FAQ that looks very much not Microsoft approved. So that’s a good sign.