You mention below that as long as it isnt over 58.4 v fully charged I should be ok, so when I up grade to lithium can I have 18 cell pack at 3.25 volts per cell x by 18 cells = 18 x 3.25 =58.5v.
Yes, but you would be carrying around a lot of dead weight for not much gain. You could be undercharging your pack and you wouldn't know.
About the only over-voltage you can safely get to is 17 LiFePO4 cells in series - 3.60 V x 17 = 61.2 V. This is at the absolute limit of the bike's capabilities, as everything onboard has 63 V caps. Any higher they pop.