You should not need $16k in lithium batteries for critical load backup of a water pump. You can get 5kwh rack batteries for $2k that will last 20 years in stand

You should not need $16k in lithium batteries for critical load backup of a water pump. You can get 5kwh rack batteries for $2k that will last 20 years in stand by applications [1] which should run a well pump for about 5 days under typical usage (30 minutes per day), if you spent $16k you would have 40kwh of battery capacity enough to run everything including the A/C in your typical home for a full day. Not sure what the permitting / venting issue would be with VRLA (sealed lead acid) as they are used in UPS's everywhere and only vent gas under extreme overcharge conditions. However if I where getting new backup batteries I would definitely go with LFP due to less space used and extremely long cycle life while being very affordable, they also have much more usable capacity than a lead acid and a much flatter voltage curve. I replaced my lead acid in my RV and got 4 times the capacity in the same space at half the weight and I should never have to replace them, they will probably outlive the RV. The biggest failure mode with both solar systems and battery systems is the electronics components of the solar controller / inverter and battery BMS. The mosfets or capacitors or digital controls seems to fail much sooner than the solar panels or lithium battery cells. Not sure if its just using cheap components to save money or what, but it definitely helps to oversize the controller, inverter and battery BMS's. Would be nice to see GaN or SiC FETs and components in residential solar equipment. [1] https://www.us.sokbattery.com/product-page/sok-48v-100ah-server-rack-lifepo4-battery https://www.us.sokbattery.com/product-page/sok-48v-100ah-ser...