Wow, that's sad...if you have to traipse around with a battery. I want to ride into town, lock it up and spend two hours shopping and sipping coffee, then ride back home.
It's peace of mind knowing that some lowlife/scum doesn't try to nick or damage the bike, if some one thinks that the battery may have some value then it could be wrenched or kicked off causing more damage then it worth. Problem is today where ever you may live there are scum around, I usually only leave it for 15/20 mins whilst I pop in to Sainsbury's for a quick shop. A frame battery is obvious and makes a bike stand out more even, my dull grey unclean 700c Norco is the only bike I leave for any length of time.
Leaving your bike for 2 hours locked up could be a risky business, it only takes minutes and a group of lowlife around a bike to become an expensive bill. Some one else always wants what's yours even if you feel you live in a good area/neighbourhood.
Recently (a few months ago) a new poster enthused about her new bike and how pleased she was with it and how it was kept safe indoors, the same week she wrote how some one had forced the front door and said bike was gone. Ownership lasted about 5 days you just never know who's about.