Googling this question leads to a lot of chromebooks with 8-12 hours of battery life at a cheap price range, and a few Windows/Qualcom Snapdragon laptops with 24 hours of battery life but much more expensive. I would love to see a linux or chromebook laptop with 24 hours of battery life at a reasonable price point but am perhaps not doing a good search.

Would any of you know of a really long lasting ARM-based laptop at a reasonable price point?

Make it yourself. 
I now us the Khadas VIM3 for that with a big RavPowe 26800mAh  Power Banks. Either a 7" or a 13" display.

With the small display, one powerbank is enough for about 15 hours. Big display is a little less than 10 hours.

I charge my power banks with solar panels. So I always have power.

The Pinebook pro should be released one of these days. It's only got a 10 000mAh battery, but if you bring a power bank wih you it'll last a long time.
Greetings.


 

Just received my Pinebook Pro this week. I get roughly 8 to 10 hours of battery life out of it with moderate usage. It can be charged/powered from a micro USB-C port, so a power bank will extend battery life.

 

Performance is actually good, especially for the price.