I hate to say it, but the only time I ever ran out of juice during a show, I lost my file. It was before I ever used an external source. All attempts at restore failed. That said any time I use an external battery source, I usually end up with a totally full internal battery by end of show, because it is charging the battery while it is recording. So if my external runs out, the internal takes over. That said, if the external was not delivering an accurate 5v charge, it could cause some problems, or not function the same way.