You might very well be right on keeping an N7. I’m glade I still have it as my backup. I have one of the retention devices, a snugfit I think because the processor was falling off my ear. At first, I switched from a medium ear hook to small, that worked temporarily, but I needed more security. My snugfit works. My coil can come off and I won’t lose the device. The coil as you can see has a lot less bulk on the N7 de which is why I can lay on it. If you keep the N7 as a backup, I would suggest some retention if you are going to be active with it, just for securities sake.
It was Cochlear that advised me to go up one size on the magnet because of the weight of the K2. I’m just thinking of getting a size 5 because of the thickness of my hair for when I wear on top of my hair. The hair clip keeps me from losing the device.
Battery life with my K2 is about 14 - 15 hours. I easily can go the full day and still have like 40% left at the end. The battery should have a lifespan of 5 years. Very happy with the battery life. I also can use my N7 battery all day, I think that battery has a 9-10 hour life span, but I still need to verify if I have the regular rechargeable or the compact one. In case you are curious about the N7 battery.