people are convinced replaceable battery makes the phone bigger. yet somehow those people dont mind walking around with the phone AND an external battery pack. wow
Because a removable battery pack doesn't need to be carried everywhere or in your pocket. If this was about making it through 1 long day, yeah I'd find it annoying to go out with my friends all day in teh city and have a battery pack and in that case I would prefer a spare battery.
However, since I carry a backpack to work, I just lump my tech goods (spare charger, battery pack, tablet) all in my backpack. Its not a big deal. In that case, where my phone is just in my pocket, I would prefer a smaller phone in that case.
With that said, to answer the OP, its likely his GB phone even with fresh batteries won't last as long as phones today will. Newer power efficient SoCs and modems and LTE radios help make things a lot better now. If you need to keep your phone over 2 years, then perhaps I can see removable batteries being a good thing, but if you plan on upgrading every 2 years, it shouldn't be a problem. My iPhone 5 is running well still, although now I consider the battery crappy having finally moved out of Nexus battery land and having a true behemoth to stack up against the iPhone.
To me removable vs non-removable isn't an issue if the phone can get me through one day use. And by one day, I don't mean at the office where you have the luxury to plug in. I don't even plug in because to me my phone SHOULD be able to last without a bump charge. The true test to me is a weekend when I'm out and about and NOT able to charge.