I think I should go with the 48v 15ah as well but I keep changing my mind. The bad thing (or good thing) is the ping batteries last forever, 3000+ cycles so whichever battery I buy it will last me a long time.
I'm not too sure if I need two 36v 10ah and making them 72v, that would be way too fast I think.
Anyone on here own a 36v battery? Are you satisfied with the speed or do you wish you went with the 48V battery? I think I need to buy the right battery the first time because if I end up buying another one it would defeat the whole purpose of going car-free and saving money.