At the start of shooting a community event I turned my 50D on and nothing. Aaarg! I popped the battery out and re-inserted it and then it was fine. Battery was Canon brand and fully charged and I'd test fired the camera before leaving home. Camera bag is well padded. I baby it. I've tried to make it happen again but the battery door has to be clicked open for it to turn off and I'd swear it was fully closed. Since I use it in my business is there anything I should do other than always have a backup camera with me? - clean terminals etc?