It is hard to believe that there is no provision for retention of the batteries, on any vehicle. Certainly batteries must be secured on any road vehicle in the UK/EC.

Is it possible to check with the manufacturer that nothing is missing/modified on this truck. Perhaps you could let us know the make & model so that other visitors can check their trucks?
Do you have a Government safety organisation you can refer the matter to in the event that this truck is "as supplied"?