Time to resurrect an ancient thread.
I have been doing a lot of reading about this whole BMS vs no-BMS thing. The main proponent of no-BMS is Jack Rickard, who has been deemed a "heretic" by many in the DIY EV community. He initially bottom balances each cell manually (using a 50W 1/2 ohm resistor) to anywhere between 2.7-3.0V and then charges the pack to an average of 3.6VPC. Some end up at 3.5V (ones with more capacity), some end up at 4.0V (ones with less capacity).
He claims to have run his car for years without the cells going out of balance, never having to rebalance. He even claims that over time, the cells "grow into each other" and become more balanced on their own, though he admits his evidence is merely anecdotal.
I liken charging/discharging lithium batteries to filling/draining a bunch of slightly different sized glasses with water, each at exactly the same rate. When starting with them all empty, some will fill to the top, some will not. The important thing is that they all drain down to the bottom at the same time, every time.
Jack argues that the bottom is where cell damage happens. Overcharging obviously isn't good, but it only damages cells slowly over time. On a top balanced pack, cells reach the knee (the quick drop in voltage just before the cell is totally discharged) at different times. So if a cell falls below 2.5V and has no jam left but there are still other cells with some jam remaining, they force current through the fully discharged cell and toast it in short order.
Bottom balancing allows every single cell to reach the knee at precisely the same time, with ample warning. No chance of strong cells destroying weak cells. Also, Jack argues that with bottom balanced lithium, a voltmeter IS an effective way to determine DOD. A good Ah counter/fuel gauge is obviously a recommended tool to use as well, and they are available for $75-150.
It is amazing how heated the BMS/no-BMS discussions are.
Bottom Balancing - DIY Electric Car Forums