If you keep the BIN on your memory card, the firmware will be automatically installed (if needed) on your batteries as you use them. DJI recommends always keeping the BIN on your memory card, but it's okay to remove it if you're sure all of your batteries have been updated.What about when using a new battery?
Except that it's quite a good idea to format the card periodically, rather than just deleting files.If there is a battery update and all batteries haven't been updated, it's good to keep the firmware on the card. It doesn't hurt anything to leave it there until the next update.