Device is likely the wrong node to start with. Event state and trigger node are the two primary starts to a flow. Use a trigger node and put the power entity where shown. Set the state to > 2000. Take note of the drop downs set to number
From there a current state can check the battery level > 50 and the node will fire from the top. All nodes that evaluate to true fire from the top.
There is also a turn off sequence in the below
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