1. The problem states that on average 138 out of 150 batteries are charged. 2. We need to find the probability that a purchased battery is not charged. 3. Probability charged $=\frac{138}{150}$. 4. Probability not charged $=1 - \frac{138}{150} = \frac{150-138}{150} = \frac{12}{150}$. 5. Simplifying $\frac{12}{150} = \frac{2}{25} = 0.08$. 6. Therefore, the probability that the battery is not charged is **0.08**.