Taking the battery down to zero percent is kind of asking for trouble. A real quick slip and it's undercharged and now dendrites are forming and you are causing great grief in your battery pack.
There is no real NEED to do it. Balancing happens on the top end of the battery. You do NOT need to discharge it to balance it, the balancing happens at the upper end. Ideally a balancing cell should be active ALL THE TIME. When working properly, they would draw milliamps when idle and keep the battery cell voltages within 50 mv of each other on a very tight equalization. it's essentially a wheatstone bridge, and as soon as one of the cells dips a bit, the bridge unbalances and current trickles to the low from the highers to balance them all. Typically a 5 amp current can flow with a beefier balancer. It does its thing and turns off, run the bike hard for a few minutes, minimal inbalance, the balancer trickles it back to balance, shuts off. it should be for the most part, an out of site out of mind device.
Pushing batteries to zero and 100 is not good to be honest. it stresses them. going to 80 percent charge would be the 'center' range, so from 10 percfent to 90 percent of capacity. is where you run them at for the better longevity stats. If you ran it even 70 you'd get probably double your cycles again out of the battery.
Also you have to remember with lithium. A cycle is a FULL CYCLE . NiCd NiMh, you run it down 30 percent and back up, that's a cycle, down 50 percent back up, thats a cycle. down 70 percent recharge, thats a cycle. down 5 percent up to top. THAT is a cycle.
With Lithium tech now, you run it down 30 percent and back up. that'd 30 percent of a cycle. down 50 percent and back up, thats an additional 50 percent for 80 total percent cycle now. now down 70 and back up, thats now 1.5 cycles total now... instead of 3. It's a much better chemistry in many ways here.
Hope this is not clear as mud... If anyone cares, Ivce been doing solar / batteries since 1986, way back before it became cool and was just nerdy,so have a small idea what I am talking about.
Aaron