One interesting feature on Samsung's flagship phone is the Wireless PowerShare reverse wireless charging support. This is supported on devices like the Z Fold6 and S24 Ultra. But if you buy Galaxy Watch Ultra and Watch7, Wireless PowerShare cannot be used to recharge the battery.
According to Samsung's FAQ page, the change to the new BioActive sensor used on all three watches requires a different bottom panel design. As a result the new wireless charging sensor is not compatible with the one used for Wireless PowerShare. However, the charger used in the previous model can still be used.
It's a disappointing decision for those who regularly use their smartphones to charge Samsung watches but it's a decision that needs to be made to ensure better health tracking is possible.