I’ve put an ESU small Powerpack in mine as it was a v4 chip and and changed the cv’s to set the backup time to maximum a couple of years back. It’s fine if the wheels and track are clean too.
An extra £40 to solve, but better that than the loco sitting in a box for what is otherwise a nice model in my view.
Also check for fluff around the power axles where they join the wheels. I recall that added to the problem.
Best of luck