Same problem here. Bought the cargo train set 60052 as a reward for my young daughter, discovered it took 9 AAA batteries so I had to duck out to the shops at dinner time to avoid disappointing her, unfortunately I bought the infamous Duracell AAA's with the large positive posts, went through the whole process of building the loco and putting the batteries in... tried to turn it on and NOTHING. The last couple of hours have been spent troubleshooting the whole electronic unit out of the train, eventually swapping out batteries (for another packet of duracells though, doh!), and finally found this forum thread and tried some other branded batteries which I took out of TV remotes in the house. They didn't have enough juice to run the train but at least the battery box turned on! So I had to carefully cut some strips of aluminium foil and fold them into the positive end of the battery box to use the Duracell's again. Daughter went to bed hours ago disappointed, but at least she'll be able to run the train in the morning. Massive design flaw by Lego to put the metal contacts behind a plastic cage!!!!