Try the user manual if you have (try Celestron web site). I did find this;
https://stargazerslounge.com/topic/2...ron-8se-power/
Note there is nothing stopping the user from accidentally or deliberately reversing the leads on the battery thereby reversing the polarity of the Celestron plug no matter how it’s marked. That’s why I suggested a small multimeter to test the powered plug before you connect to the ‘scope. To test connect the leads to the battery and make sure centre reads positive with respect to outer of the plug. If you’ve never used a multimeter I suggest you get someone else who has to help you because if you hook it up incorrectly you could get a false result.
I’m not familiar with the Celestron lead and for the price I would expect there to be a fuse inside the cigarette plug. If for some reason you are getting no voltage then check and/or the fuse, (with exactly the same rating).