While connecting an external battery to the R4's power plug is most convenient, there is a liability if connection is momentarily lost when recording (maybe also when playing back) that your data, and sometimes also HD/flash memory storage, will be corrupted to not be usable, and this even if having working batteries inside the deck.
While this is not a concern or liability with some other decks, the R4 does
not gracefully handle power source switching.
So suggest being most careful any external power connection. Take care your connections will not (even for a fraction of a second) drop out. Like with power plug rotation, a tug on the power cord, or any other circumstance causing external power disruption while the deck is running.
For this reason I
only offer external R4 powering solutions using internal dummy battery connection that's not as convenient to use, but most reliable to never cause disconnect tragedy.
See my page for reference purposes at:
www.sonicstudios.com/batsys98.htm#bd8