DRAFT: TO BE REVISED ;-) (FB)
Batteries can give you many different outputs (!?) depending on how they are wired up. As long as you don't have to worry about weight you could try endless methods of wiring different types of batteries to get a desired output.
Wiring Batteries in Series
Wiring batteries in series is a great way to increase voltage, as you can see on the diagram below the voltage is added up in each cell which then equals its output. The mA/h does not change when batteries are wired up in series.
The only problem with batteries wired up like this is that they are prone to faults, were you end up with a 'dead cell', this means that when you are charging/discharging the pack there might be one cell that doesn't hold its charge as much as others bringing the overall capacity of the battery down.
Wiring Batteries in Parallel (DON'T DO IT!!)
When batteries are in parallel the mA/h will increase (not the voltage). Remember:- the mA/h does not mean the current going through speed controllers etc. it is only a guide to the maximum current a battery can except where it will last for one hour.
Theory About The Whole mA/h Thing!
Just think of the batteries being a tank of liquid, when the liquid runs out the battery runs out. Below are four diagrams:-
The height of the liquid in the tank increases the pressure/voltage at the bottom.
The area of the liquid increases the overall capacity of the tank/battery.
The number of amps the motor can draw is not limited to mA/h of the battery, the mA/h is only a guidance figure to tell us how many hours it will take before the battery/tank runs out.
If you really wanted you could let out 10 Amps worth of liquid, just that the battery wont last very long unless it has a larger capacity.
In Car Terms
The diagrams below explain the differences between the size of the tanks and the distance that can be traveled.
5 Gallon Tank = 1000mA/h Battery
10 Gallon Tank = 2000mA/h Battery
If you have a car with a small fuel tank it might do say 100 miles at 50MPH. if the same car had a larger tank it may do 200 miles at 50MPH.
The size of the tank does not effect the speed the car does, but it will effect the distance it can travel.
DO NOT MIX BATTERIES OF DIFFERENT TYPES!