This is extremely risky, complicated, and dangerous. Different chemistry batteries have massively different impedance curves under load and at different temperatures This thing might start off at roughly the same voltage, but there's no way it'll stay that way.
Say this add-on pack sags 1V below the monolith and the wire resistance of the wire between the two battery packs is 5 milliohms. You just dumped 200A into your range extender, and either blown the fuse, the connector, or damaged your add on pack. And this could happen as soon as you try to draw a load.
Connecting it to the same bus without careful consideration of impedance will cause very bad things very fast
Only one person(outside Zero) has added batteries to expand range, but he used additional Zero batteries with the same chemistry. Zero's batteries have mechanical contractors and battery management boards designed to disconnect them under any unsafe condition.
The fact that you're asking this on this forums suggests that you do not have the knowledge necessary to do this safely.