The way I understood the reasoning for the higher capacity battery in the two new HF coils was because the primary use is gold hunting. With that sort of thing, you might be hunting for a couple days at a time, in a remote area, without easy access to recharging. So the higher capacity battery is so you can do that, without having to worry about recharging or carrying an external battery backup.
Higher Frequencies do use less power, so the battery will last longer anyway. Moving the battery outside the coil, I believe was mostly due to space limitations within the coil for a higher capacity battery... and not the battery replacement process. Which should only be necessary every 5 years or so with normal detecting and even then, it cost $50 to send it in and have it replaced.... that's not too much when you consider the savings the lipo battery gives you over those years.
I've had my Deus for about a year and a half, hunt with it weekly and always recharge it after each hunt. I have no noticeable difference yet in my battery life and even when I hunt for 10 hours a day, the bars are still at half way or more! The batteries last so long, I even leave it on when I take breaks so I don't have to power it up and set the GB again. ha