Your question is a bit light on specific context. One particular distinction here is if your A-state machine and B-state machine can be abstracted into a common ancestor, the base-state machine.
Specifically, are you able to abstract all of the state machine features that A and B use, so that the logic for A using its AStateMachine is exactly the same as B ...
One way, focusing on the light and button. Viewing the power system as a separate concern.
| current State | event | new State |
| Unpowered | press button | Unpowered |
| Unpowered | powered | Off |
| Off | press button | On |
| Off | unpowered | Unpowered |
In a finite state machine with no push down stack, all state is encoded in... the states.
You have several different dimensions I can identify:
Battery state: depleted/charging/charged
Plgged-in state: unplugged/plugged
Device state: on/off
You can imagine a 3D chart that has one cell for every possible comination of battery state, plugged-in state and ...