Paralleling Multiple Packs and the use of Diodes
Three basic rules of thumb:
If you're not using a BMS on the packs, and they are the same chemistry and number of cells, you don't need diodes.
If they are different chemistries, and have different voltages and/or discharge curves, you would want diodes.
If they have a BMS on each pack, you would probably want diodes, dpending on how the BMS is designed.
For specifics and further discussion of details of why these are the case, see the various Endless Sphere threads on the subject (links needed, also need to copy relevant data from there to this article).
parallel battery simulator