How far apart can 2 battery packs be from each other & work?

I have been using one 9 cell (27v) prismatic lifepo4 pack I built a few years back attached to the rear rack, and I have 3 more cells for making a 36v pack but they are heavy 30ah cells; if it's not a big deal I'd rather distribute the weight by making a 2nd pack out of the 3 remaining cells and attaching it to my front rack and joining the power supply to the bms. Is this doable or is the distance too far in between them?

As long as the wires joining them are big enough it's no problem... It maybe might lead to a little more balancing needed if it changes the current sharing somehow.

Agree, just use some big wire so there is not a lot of heating going on in the wire, costing you drain from half the pack, or other unintended effects.