“Small Pack” = Four 22.2 volt batteries.
“Big Pack” = Eight 22.2 volt batteries.
If you care about the technical details here’s a short guide. We call the small pack a 12s2p configuration, and the big pack a 12s4p configuration. This means that the small pack has 12 Lithium Polymer (LiPo) cells in series, which increases the output voltage to around 44.4 volts. Since you can’t buy 12s batteries for a decent price we use two 6s batteries in series, which is the same as having a 12s battery. I’ll call our two 6s batteries a “battery pair”.
Now that our battery pair is outputting the voltage that the system runs on, we can then add more of these pairs in parallel. By running them in parallel we can double the runtime of each battery pair, and reduce the load placed on each pair. Note: most of the batteries we’ve looked at so far do not output enough current to support the OpenPPG (300A), so we need a minimum of two battery pairs. From there you can keep adding 12s battery pairs until your legs break from the strain of carrying them all.