I'm assuming you want these variables to be global, ie to be in scope and visible in all your source files?

If that is the case you should define each variable exactly once in one .c file, eg:

unsigned char a;
or, if you want to initialise it:
unsigned char a=5;

Then, in exactly one .h file you should use:

extern unsigned char a; //Note: no initialiser

This .h file should be #included in every .c file that references the variable.

What you have done by declaring the varaibles as static is made them NOT extern, ie they aren't exported to the linker. This means that you now have multiple, separate copies of the variables, one in each .c file. This certainly stops the linker warnings but is not, I think, what you want.