cf666 said:
It comes with a 24v 6ah battery which only gives me 144W out of the 250W available in the motor it comes with.
The 144Wh (the H is extremely important!) of the battery has nothing to do with the 250W (note, no H) of the motor.
Wh is capacity
W is power
They are unrelated in the way you're thinking.
If have a wattmeter you can check to see if the system is actually ever even drawing 250W from the battery. Without that, you don't know what power you're already using, and so you don't know how much more you might need. (though there are calculators on teh web that will tell you how much power is needed to go up a specific slope at a specific speed, which will give you a rough idea of what you need. There's a number of threads here with Calculator in the title or first post that may have lists of those, or a regular web search for bicycle power calculators).
The controller is what limits power to the motor, so if the controller's current limit is too low, it won't let the motor draw enough power to do it's job. But it also protects the motor from overheating, so if you use a controller with too high a limit, you can burn up the motor if you put too much load on it for too long.
To see the relationships between the battery, motor, and controller, you can go to http://ebikes.ca/simulator and read the entire page, then play with different setups to see what they do.
The little board inside your batteyr is probably the BMS that protects the battery from overcharge or overdischarge or overcurrent.
The cntroller is usually a little box somewhere else on the bike, sometimes built into the motor casing (especially if it's a middrive rather than hubmotor).
