Welcome back:
The voltage shouldn't drop that low. If I recall, the electronics require a minimum of 9.6v to function. I suspect the starter is bad and drawing too much power. However, before you replace the starter, take a socket and breaker bar and confirm you can manually turn the engine at the crankshaft. I doubt there is an issue, but something could be preventing the starter from turning the engine. For example. A head gasket could have allowed one of the cylinders to fill with coolant which would prevent it from turning.
Again, I really doubt that is the issue. If the starter did the same thing even when being jumped, I bet it's bad. Once it is removed, you can have the parts store bench test it for you to confirm it is the problem. That way you don't spend the money to purchase a new one only to find it isn't the issue.
Please understand that I am still assuming that the battery is good and all connections are clean and tight.
Let me know what you find
Joe
Saturday, September 21st, 2019 AT 10:14 PM