To simplify the expression \( 5^9 \cdot 5^{-13} \), we can apply the properties of exponents. According to the property \( a^m \cdot a^n = a^{m+n} \), we can combine the exponents:
\[ 5^9 \cdot 5^{-13} = 5^{9 + (-13)} = 5^{9 - 13} = 5^{-4} \]
Now, to express \( 5^{-4} \) with only positive exponents, we can use the property that states \( a^{-n} = \frac{1}{a^n} \):
\[ 5^{-4} = \frac{1}{5^4} \]
Therefore, the equivalent expression with only positive exponents for \( 5^9 \cdot 5^{-13} \) is:
\[ \frac{1}{5^4} \]