The NiCD's (or NiMH's) will get hot, but generally they are safe - when I talk about batteries fizzling, I was hitting them with a 3.5A charger, not the 400mA wallwart that comes with the tank - If you have a better charger that can handle Ni batteries, then I'd use that to be honest.

The bulldog also requires you to unscrew the smoke unit to get the top off, so in addition to the 6 main ones close to the tracks you'll need to undo a group of 1 to 3 screws at the rear (I just checked the 3 bulldogs I have here - they're all different! ) If you look at the picture above, you can see the smoke unit is attached to the top via the smoke tubes, and the 2 screw pillars in the chassis that it sits on - you don't need to screw it back down necessary when you close the tank, but you will need to remove those screws to get it open.

Things to check for:
The single single wire going to the little exposed (receiver) board is properly attached - it goes to the aerial base in the turret.
Gently tug the wires going in and out of that little piece of heat shrink tube you can see on the black wire in the picture - there is an electrical connector under that, and sometimes it gets loose.
Finally, make sure that electrical connector is properly covered by the heat shrink tube, as some times this can come loose and expose the connector and short the aerial out.
Visually inspect the motor wires and make sure there are no shorts between the terminals on the motors and the neighbouring gearbox frames.
Make sure the 3 wire cable going from the receiver to the main control board (probably has a black case, if not you have an older one somehow) is not tangled up with the power cable or motor wires (EM interference).

If all of that looks good, and you have taken out the crystals in the transmitter and receiver and reinserted them, then you are probably looking at a duff tank

Anybody else got some suggestions?