A 72v Geo Metro, now that's familiar...
That's the problem with someone else's car- too many questions. Your pack is only as good as your weakest cell, so it might just be one cell causing you problems. And I can only guess at what my range is since I've never gone further than 6 miles on a charge, but I would estimate mine is about 15 miles so that's what I would tell someone if they asked about my car. What kind of charger do you have? I'm pretty convinced that some batteries die prematurely when they are charged together from a multi battery charger- but that's just my personal opinion. I would definately take a bunch of voltage readings before and after charging of every single battery. And personally, if it were my car I would charge each battery individually with a 12v charger and see how each battery behaves individually. Then, when you get more familiar with them, you could switch to a multi-battery charger. Good luck, and I know from experience that you have a great car on your hands. The Geo Metro seems an ideal choice for a conversion.