I decided to go whole hog on my Bosch Fat Packs BAT836 36V batteries (BFPs) and fit 8 of them into my rear Topeak Expedition MTX bag. I took each of the 8 packs and disassembled them by removing the end bumpers which are plastic with a rubber coating and remove the extrusions that were not needed from the red shells surrounding the packs to reduce their size. I may do more, but with what I did, I was able to fit all 8 in.
First, the removal of all of the security screws, ends and protective end caps.
Then I used my Lie-Nielsen adjustable plane to shave off the parts I didn't need from the BFPs into a gardening planter bowl!
Then came the bundling of the packs together and of connecting the group of 4 Anderson Powerpoles that I needed for each pack. The configuration that worked the best was in a 1 flat pack over a 3 stacked configuration.
finally, putting them into my Topeak rack bag and zipping it up!
It fits snugly, but it fits. I intend to run the wires to the switch which I plan on installing tomorrow that allows for switching between 36 and 72V seen here