Hi MC,
At this time the E+ will only work with E+ proprietary battery packs.
There are some reasons to doing this:
1. The E+'s LCD display can show accurate battery state of charge
information (5% increments)
2. The E+ bike system will ensure that the battery will never
overheat by limiting the power of the motor if the battery exceeds a
specified temperature (the E+ is a self protecting system)
3. EMS can warranty the operation of the entire bike system without
question
However, to your point, we are looking into ways in which we can use
off the shelf batteries in a safe and reliable manner. In the end, we
must be able to stand behind our product 100% and be certain that what
we sell to our customers works.
- You friends at Electric Motion Systems