In college I had a 1984 300ZX I loved. I wanted it faster though. I spent a lot of time trying to get shops to quote me prices on adding a turbo charger. They kept telling me over and over, just sell the car and get the turbo version which already existed. Somehow at age 18 this did not make sense to me. I didn't want to get rid of my car, I just wanted it to have the turbo! How dare they suggest I get rid of my ____! (I think it had a name but I cant remember) Although a year later I did sell the car and get the turbo one, and instantly it made sense this was the right thing to do all along.
about 10 years ago my mom had a long commute and was complaining about gas prices. My Dad and I bought her a 2001 VW TDI that got 50 mpg. She said she loved her car and didn't want the new one. It took a lot of effort, but as soon as she finally drove the VW for the first time, she said she liked it better and we sold her old one.
I could tell story after story like this. There is a personal attachment we all form with our vehicles. It's almost like a relationship. The thought of depending on something new and unknown becomes something feared because it is unproven and we are conditioned to form a bond with something that treats us well despite how irrational the logic might be.
My point is, for all of you wishing to get more range by swapping battery packs, this would likely cost 2-3 times more than the difference than if you just sell your 2014 Zero and buy a 2015 with the bigger battery. Although I totally understand. Your current bike is amazing to you and you don't want a new bike, you just want to make yours a little bit better if possible.
The battery is perhaps the single most costly item on the bike. Even if you bought a new one, what do you plan to do with the old one? Even being the huge big time hacker I am, I saw this thread and thought to myself that it sounded somewhat illogical to consider vs just upgrading the whole bike. The main reason as Aaron above mentioned is the cost.
The best way to "break out" of the current thinking, and see the other options is go to your local dealer and test ride the 2015 Zero for a good long test ride. That will instantly break the psychological barrier you have trying to improve your current bike, and you will start thinking about upgrading to a new bike when the time is right and you feel you need the additional range. It's like you are taking the 2015 Zero on it's first "date". If the "date" goes well you can't help but think about it. However, if the bike you are currently "dating" is taking good care of you, you are happy and don't have any desire to think about "dating" any other "bikes". It's a good thing we think this way. If we didn't, our world would be a mess.
Anyway, no matter what bike you have, bottom line is: Go test ride the 2015 Zero SR! I can guarantee after your first "date" you will want another.