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That is basically what I have found as well. Voltage alone can not be used as a low charge indicator (works fine as a high charge indicator through). That is why I am planning measuring amp hours used for the low charge indicator. There will be a fairly large factor of safety built into the calculations so that the batteries can only hit ~80% DOD. They also aren't being fully charged either to increase cycle life. Thankfully I have excess capacity in this case and pushing the batteries to the limit isn't necessary.
With this method I don't see a reason to individually monitor each cell. The one thing my BMS system does not do is active balancing. The pack will be balanced at the bottom before it is installed into the car. In time I'm sure the cells will drift and another balance will be needed to restore proper performance. Time will tell how long this will take.
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