System information

• Steam client version (build number or date): 1671133277
• Distribution (e.g. Ubuntu): Steamdeck Holo
• Opted into Steam client beta?: Yes
• Have you checked for system updates?: Yes

Please describe your issue in as much detail as possible:

SteamClient.System.RegisterForBatteryStateChanges isn't consistent with other RegisterFor that return an object with an unregister function.

Steps for reproducing this issue:

1. Set return of RegisterForBatteryStateChanges: var registeredObject = SteamClient.System.RegisterForBatteryStateChanges(function)
2. Attempt calling unregister: registeredObject.unregister()
3. registeredObject is undefined