I think it's easier to go with the extended battery (although I have the dock too) so that you don't have to take the cover off, swap the batteries and reboot the phone.
It's hard to say which is the better way to go, two lightweight batteries or one extended battery. With the extended battery, the phone just keeps going without having to replace a battery, pulling the back off and having to reboot the phone or having to carry an extra battery. The problem carrying an extra battery is that it has to be in a pocket with no coins that might short the terminals and not in the same pocket as the phone so you don't scratch the phone.
On the other hand, having two thin batteries keeps the thin form factor of the phone and keeps the phone light. I've got 2 regular batteries and a heavy duty battery, so I can go either way.
Settings > Wireless & network > Mobile networks > System selction > CDMA mode. I am sure by default LTE automatic is checked.
I have chargers everywhere I am. My battery is always around 70%-100%, lol I have learned Smartphones batteries never last very long.
I think I might get the dock with the extra battery and leave that at work. Then, I could just swap batteries at lunch or so and always have one on standby. That's where my big battery drain is. My office is like a bunker, so every phone I've had dies fast.
I understand the "bunker effect", because the buildings where I work are hard on a battery. I bought the extended, can get 12 hours out of it while at work, and more when not there. Usage is still the key for longer times.
As for a case for the extended, the Verizon holster for the kickstand case/shell holds the phone with the extended battery very well. I've used it for several weeks and it has not slipped or fallen out, once. It is actually a little tough to get it out until you "learn" the process.