The Panzer-Ersatz-Abteilung (Fkl) 300 was formed in September 1942. It was redesignated Panzer-Versuchs-und Ersatz-Abteilung (Fkl) 300 on 9 March 1943.
It was the replacement unit for all panzer funklenk-units.

The "(Fkl)" in the name was for "Funklenk", a reference to the radio-controlled demolition vehicles used.

Order of battle (Sep 1942)

Stab
Panzer-Ersatz-Kompanie
Lehr-und Versuchs-Kompanie

Order of battle (Jan 1943)

Stab
Panzer-Versuchs- und Lehr-Kompanie
2 x Panzer-Ausbildungs-Kompanie (Fkl)
Ersatz-Kompanie

Sources used

Markus Jaugitz - Die Deutsche Fernlenktruppe (2 vol)
Thomas L. Jentz - Funklenk Panzertruppen (in AFV NEWS, Sept-Dec. 1986, Volume 21, No.3)
Thomas L. Jentz - Panzertruppen (2 vol)
Georg Tessin - Verbände und Truppen der deutschen Wehrmacht 1933-1945