Impossible to answer, since every loco, layout, and engineer varies.
This is why I am asking a specific question, amp hours is amp hours. If you tell me what you have and if you are pleased with the run time, that helps.
Do you have any experience how long your loco runs on a full charge?
Greg
(where I am headed is put as small pack in the loco as gives you satisfaction for run times... any additional weight from larger than needed batteries is sort of wasted. The only desire you have communicated is to pull more cars.)