harddrive123:
The reason you use lithium batteries is because they give very high current with small form factors.
The reason to use lithium batteries is not usually the high current (nickel-cadmium is usually at least as good), but high energy density - for size and for weight. Generally, nobody wants it to be any bigger or weigh any more than it needs to.
There are other criteria - nickel-cadmium batteries self-discharge relatively rapidly.