Robot car motors, amplifiers, batteries

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Hello everyone, I would like to build a robot car but I'm unsure about some things. These are the car motors I would use:http://www.ebay.com/itm/4PCS-Smart-Car-Robot-DC-Gear-Motor-3-9VDC-For-Arduino-Compatible-/171065233087?pt=LH_DefaultDomain_0&hash=item27d4484ebf

The part I would like someone to explain is connecting amplifiers and a rechargeable battery.

I've found some amplifiers that I think I could use for this:

http://www.ebay.com/itm/Dual-H-Bridge-DC-Stepper-Motor-Drive-Controller-Board-Module-L298N-for-arduino-/251080674810?pt=LH_DefaultDomain_0&hash=item3a75930dfa

I've found this battery:
http://www.ebay.com/itm/1-pcs-7-2V-3800mAh-Ni-Mh-rechargeable-battery-pack-RC-Tamiya-Plug-Charger-/380851627560?pt=LH_DefaultDomain_0&var=&hash=item58ac86a628

I would connect the amplifiers to an atmega microcontroller. Would the signals have to be pulse width modulated signals?

Could someone please explain if I found good parts for the job and how to connect them together? Is the battery voltage and amperage alright? Should the voltage and amperage be different? What is the difference between a low mAH and high mAH battery ie will the motors be able to run longer if the amperage is higher? How many amps would I need to run all for motors at low speed, medium speed, and high speed? Is it:
Voltage DC 3V DC 5V DC 6V Current 100 MA 100MA 120MA
times 4? So to run the motors at 6V and 120MA I would need 4*120MA=480MA, so a battery with a minimum of 480MA? Also, is it alright to use a 7.2V battery if here it says 6V or does the amplifier reduce the voltage to 6V?

Is it possible to calculate how long the motors will be able to run at a certain speed? Would I need two batteries, one for each amplifier or would be possible to run 2 amplifiers, that each connect to two motors, using just one battery?

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Ok the mAh rating is rhe amount of current per unit time. Eg a battery of 1000mAh could run a motor that draws 1000mA for an hour or a motor that draws 500mAh for two hours and so on. In reality it is a bit more complex, especially if you draw very high currents.

The h bridge units will expect pwm. Running a 6v motor off 7.2 V should not be a problem.

With the 3800mAh battery, you could expect a run time of around 4 hours for your four motors. You should need only one battery.

Surely out there in the interwebs there are sites that show you how to connect your stuff up - just about everyone that builds a robot does it.