Only slighly off topic... Node-Red - how to build a text string that referenced a msg.payload

Well, in the first instance, I'd drag in a 'function' block and add the following code inside it:

msg.payload = `Alert, the button was pressed. This is the ${msg.payload} press since power cycle.`;
return msg;

And for the second option, you can use flow.get/set:

Add a function block to the battery message

flow.set('battery', msg.payload);
return msg;

Add a function block to the click message:

msg.payload = `Alert, the button was pressed. This is the ${msg.payload} press since power cycle. Battery level is ${flow.get("battery")}`;
return msg;

Hope that helps!