To add the two numbers, you combine them as follows:
\[ -6.54 + (-2.23) = -6.54 - 2.23 \]
Now, we can add the absolute values of the numbers:
\[ 6.54 + 2.23 = 8.77 \]
Since both original numbers were negative, the result will also be negative:
\[ -6.54 + (-2.23) = -8.77 \]
Thus, the final answer is \(-8.77\).