I tried to override stackable state for the stock batteries and found out interesting behavior: for Z-400 override doesn't work in spite of it works just fine for the other batteries. Those parts have no module so, I've defined override by the name:

    StackableItemOverride
    {
        partName = addWhatYouWantHere1
        partName = addWhatYouWantHere2
// Batteries
        partName = batteryPack
        partName = batteryBank
        partName = batteryBankMini
        partName = ksp_r_largeBatteryPack  // <== Z-400, doesn't work
        partName = batteryBankLarge
    }

The only difference between Z-400 and other battery names is underscore in the name. Can it be the issue?

I've figure it out. In case of battery packs the real name is a namespace path. I.e. for ksp_r_largeBatteryPack it's actually ksp.r.largeBatteryPack. When specified like this everything is working fine. It makes sense to add a comment in settings.cfg. Or translating dots in the part name into underscores when checking in the plugin.

Released in v1.2.4