There are three things that can be causing this problem.
1. A broken spring or stuck valve in the valve body.
2. Incorrectly adjusted passing gear cable, or the cable is faying and sticking in the sheath.
3. The retaining snap ring that holds the intermediate one way clutch has broken and come loose.
Disconnecting the battery will not have any affect on the trans as it is not an electronically controlled trans. the first thing to do would be to check the passing gear cable to make sure it moves freely. If the cable checks out then the valve body will be the next place to go as the one way clutch problem would have put metal in the pan.