Transformer question

You should only use a car battery if you are trying to put your train into orbit.

Or.... if you are trying to turn your precious $1500 Challenger into a lump of molten slag metal!

The last time you jumped a car.. did you feel your jumper cables get warm, or even hot? That's because there's too much current flowing. (fyi.. if that does happen, you need thicker jumper cables) Apply that amount of current to your train layout (even without a short) and you'll likely get the rails to the point where they'll glow this nice bright orange color, right before your plastic roadbed track melts into oblivion.

Transformers and batteries do NOT work together. At best, you'd have to build a circuit to convert the DC to AC, then go thru the transformer and re-convert from AC to DC. It's just not worth the troule.

Even using a potentiometer or a voltage regulator will not improve things in this case. There's just TOO MUCH CURRENT. If you applied the car battery to a standard 7809 voltage regulator, you're going to hear a crisp little "pop", see a tiny cloud of smoke.. and then you'd be buying a new one.

Use the 9v. Buy rechargables if you're worried about the planet or running for a long time inexpensively.