You don't need U1.
You don't need D1, with its variable voltage drop, but in its place, you would need a diode from U2 out to U2 in, to power the input in the event that you connect the battery without input power.
Once you have removed D1, set U2 to deliver 13.8v. This voltage will safely float sealed lead acid indefinitely.
Some sealed lead acid cells state that you can use a higher charge voltage if you time the over-voltage carefully. Doing this will result in a quicker full charge. Check the book of words for your specific cells.