Interesting discussion.
I hadn't considered the current draw of a balancing BMS on a LiFePO4 pack. I had thought about the (slight) risk of a balancing MOSFET failing and bringing down the pack, so I bought a simple battery monitoring system, which only provides high/low voltage and high temperature cutoff. It's always powered, and draws a few microamps. My little 4s pack loses maybe 10mV sitting in the boat over the winter with no charging at all. I'm a fan of bottom balancing, which makes sense for a traction pack, whose main purpose is to be drained by a motor and then recharged. I'm going into my third season, and the cell voltages have drifted very little.
I wanted to know the cell voltages at a glance, but didn't want powered volt meters draining them. I found little voltage display modules on eBay for two dollars each, and wired one across each cell with a push-button switch. It takes 3 seconds for a module to boot and display the cell voltage.
I also wired the solar charger to the pack through a double throw switch so I could charge the pack through the BMS (normal setting), or directly to the cells, in case I ever need to recover from a low voltage shutdown. The switch also lets me disconnect the charger completely for all those sunny days when the boat just sits there and the battery is already at a good state of charge.
My thought about commercial batteries that are bricked by their BMSs: if the warranty is expired, cut open the case and clip on a charger. Commercial failure? DIY recovery opportunity.
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