The forward made 13 appearances on loan at the O’s during the back-end of the 2012-13 season but was recalled by his parent club Millwall for the final few games where he maintained his good form and played in the FA Cup semi-final against Wigan Athletic.
Batt will report for pre-season training straightaway with the O’s and his new manager Russell Slade is delighted to have the forward back at the Matchroom Stadium.
He said: “We’re delighted to get Shaun signed up. He made a great impact when he came on loan with us and we wanted to keep him longer than we could do in the end.
“Shaun had attracted interest from the likes of Notts County and Preston so it’s great that we can get him on board.”