B19 pilot reported after disconnecting the aircraft from the charger and removing the chocks; the aircraft began to move on its own. The pilot immediately entered the aircraft; stepped on the brakes; and turned off the engine; regaining aircraft control.

Narrative

On Day 0; I was at ZZZ to go for a local flight. Aircraft X didn't start since it wasn't used for a month. The FBO was kind enough to tow Aircraft X to the front of their hangar shop and connected it to the charger. After about 20 minutes; I decided to check if it would start. Fortunately; it started; and I got out to disconnect the charger and to move the aircraft. To my surprise; when I moved the blocks; the aircraft started to move slowly. I jumped inside and slammed on the brakes. I turned the engine off. Aircraft X got very close to another aircraft that was being worked on by a Mechanic. I got out and checked to see if I had hit anything. My aircraft did not touch the other plane. The Mechanic that was working on the aircraft did not notice anything. They continued working on the aircraft. I checked Aircraft X and there was no damage. I also ensured that there was no damage to the other aircraft. I pushed Aircraft X out of the FBO repair area; cleared from the other aircraft under repair; and then started the engine. I proceeded to taxi and got clearance for a local flight.