Thanks Shawn. Yes, good to keep things as simple as possible. The complexity argument cuts both ways though, in this instance, because a failure of the BMS when you are using only one, can leave you dead in the water, whereas a single BMS out of 4 failing, and everything might be able to carry on happily while the defective one is replaced? Same consideration for protecting the batteries from damage: if a low or high temperature cutoff or voltage cutoff fails, you can have all of your cells damaged, or just one quarter of them. Over a period of 10-15 years, the odds of this becoming more than a hypothetical are something worth some pause?