I cannot find the battery compartment in percy train engine

This is Bertie the bus. It stopped working so I took it apart. The Philips head (criss-cross) screw gives access to the battery. You're not supposed to take out the screws with triangular socket heads. If you do everything falls apart and you need an engineering degree to know how to put things right.
This battery holder is clear plastic, instead of black, so I can see what is happening after assembly. The red wire broke off the motor while I was looking at it so I had to resolder it. The red plate on the upper part swivels, it has an arm that holds the clutch plates together when the switch is on. The long white arm at the upper end of the gear assembly should fit into the slot of the red swivelling plate. I think it is supposed to be a noise-maker.
Bertie is supposed to go on the road, not the track and there is a plunger that cuts out the power when it is on a wooden track. This stopped working so I jumpered it to be always on.
Good luck.

I am also looking for the same fix. The rubber is worn away!

According to the Instruction Manual it requires 6 AAA batteries, you will need a Phillips screwdriver to access the panel where you must replace it.
The remote controller and the engine need batteries.
Engine
• Locate the battery compartment on the back of the Engine. • Loosen the screws in the battery compartment door with a Phillips screwdriver. Lower the battery compartment door and insert three "AAA" (LR03) alkaline batteries. • Close the battery compartment door and tighten the screws with a Phillips screwdriver. Do not over-tighten. • If this product begins to operate erratically, you may need to reset the electronics. Remove the batteries and replace them in the toy.

http://www.fixya.com/support/t8536339-cannot_find_battery

THE BATTERY SHOULD GO IN THE BOTTOM OF THE TOY.YOU MAY NEED A REAL SMALL SCREWDRIVER TO OPEN IT.

There are apparently 2 different models of the Stanley train for the Trackmaster. One comes with a tar car and one is by itself. If you have the one with the tar car, the battery goes in that. If you have the one that comes solo, then you have to flip it over and in the middle of the bottom is a small screw that you have to unscrew and remove the middle wheels to take the top off. Once you have the top off, the battery is located there. I hope this helps.

My child has a similar train but it is a Thomas instead of a Percy. There is probably a screw on the bottom. My son's train has three screws and the one in the middle (+) is the one that opens the train so I can put a battery in it.

mcdevito75 here, I believe the battery--ies go in 1 of the wheels, try looking for a cover or squeeze 1 of the wheels for cover to pop off.

In the early model trains - Just by the middle wheel there are plastic brackets that lock the top in to open squeeze on both sides above the wheels to move the brackets in and pull the top up - This will open the top and then you can replace the battery Note my wife helped me to figure this out as I took all the screws out as well

its defective there was a recall 4 days ago