I'd work through the logic that you have already started to do ... you have now paired your phone with 2 bluetooth kits and had them both drop out.
Can you borrow another bluetooth phone and pair that with the kit? If it holds the connection then you have isolated your phone as problematic.
You are then either looking for a timeout setting, or a replacement handset!
RC
Edit to say just found an online copy of the
V525 Manual and agree that there aren't any timeout options that I noticed (and why would there?!).