Actually, item # 2 is most commonly used in the transmitter (it fits there nicely and uses all 8 AA batteries).
Do you have
this item? If so, you can use AA batteries in it as a substitute for item #1 (the 7.2 robot battery) and won't need a charger.
If you have a very old (pre 2008) kit (Starter kit),
here are some build instructions for the Squarebot. If you have a Protobot kit (2008 ->),
here are build instructions for that, if you don't have them already. Also,
this guide has build instructions for some simple projects that can be built with a Starter Kit.
Enjoy!