This thread is almost 4 months old and the OP may already have made his choice. I'll post this anyway just in case.
Battery obsolescence is a definite factor to consider when bike shopping and many good suggestions have already been made. IMO, the best is to deal with an established LBS who should be able to help with battery issues down the road. With any luck, and proper care, the battery could outlast your bike. You may well be looking at something newer with better technology by the time your OEM battery gives up the ghost. Buying a spare at the time of purchase is another good idea. Staying away from in frame batteries could also help.
If you have any DIY skills, there are several things that can be done to ensure your ride never runs out of juice.
In my case, I stick with bikes that use quality external mount batteries. The first thing I do to a new bike, or one I'm building, it to convert to Anderson 45 amp Powerpole connectors. Some bikes & batteries already use this connector but there are adapters available for other types as well.
I then mount this Anderson distribution module in a convenient place:
I can then plug in almost any battery of the correct voltage.
I can even use a cordless tool battery as a range extender:
The Distribution module is also a great place to connect accessories like headlights, horns, and USB or 12V adapters.
You can choose any connector type as your "standard" and adapt it to your needs. That way, you can use any battery of the correct voltage.