St.Kp.Gren.Ers.u.Ausb.Btl. 380 Erkennungsmarke

The dog tag or 'Erkennungsmarke' shows signs of wear. The bataillon was formed in late August 1939 as Infanterie Ersatz Bataillon 380. It trained and supplied soldiers for Infanterie Regiment 380 which was part of the 215.Infanterie-Division. In November 1942 the bataillon was renamed into Grenadier Ersatz Bataillon 380 whilst it was stationed in St.Die, France. In December the bataillon moved back to Heilbronn. In July 1944 the bataillon became Grenadier Ersatz und Ausbildungs Bataillon 380 and was mobilized in August of that year and used to form the I.Bataillon Walküre-Kampfgruppe C/V. 
In October 1944 a new Bataillon was formed which was again mobilized in March 1945 as part of Grenadier Ersatz Bataillon 525. 

A Stammkompanie was a unit that trained the soldiers. Often the soldier of this kompanie were soldiers who had frontline experience, but no longer were fully usable at the front due to injuries. Of course this changed later in the war as there was a shortage of (front)soldiers and where mobilized also.
The 'O' on both parts of the tag stands for the soldier's bloodype.