In looking at the specs the Mavic Mini battery is 7.2V @ 2400mAH...the Mini 2 is 7.7 V @ 2250mAH. The Mini 2 has higher-voltage motors....so it appears that Mavic Mini batteries can be used in the Mini 2, but at a lower performance level.
The ‘standard’ Mavic mini battery weighs 100g; the Mini 2 battery weighs 86.2g
If memory serves the two models of the (original) Mavic Mini are the international version and the Japan version. The Japan version has an even smaller capacity battery in terms of milliamp hours because their regulations limit the aircraft takeoff weight to 199 g, not 249 g. That battery is 7.2V @ 1100mAH and only weighs 50g.