The new G&G TR16 MBR 308 with the G2 ETU is in stock at Zero One Airsoft, they got for an in-depth look at this AEG... "G&Gs new ETU includes technology that will automatically stop the gun from operating if it detects the battery voltage is too low. Once you disconnect the battery it will likely still operate in guns without this technology, as those products will allow the battery to drain completely flat. This means when using a G&G gun with ETU, your battery must be fully charged or the automatic cut off feature will kick in. This feature is designed to protect your battery as well as the advanced control board inside. To avoid disappointment ensure your batteries are discharged and freshly charged before use. This is known as 'cycling' your batteries. This technique also improves battery performance by promoting battery life and memory."