When I get my Evergreen phone …
I would expect a change in battery capacity to be pretty much linear i.e. if you get X hours with a 2000mAh battery and you change to a 3500mAh battery then you should get 1.75 x X hours, all other things being equal.
I believe Dogwood will have the 3500mAh battery. Battery for Librem 5 - #45 by joao.azevedo