Wondering if anyone has done this already.
LiFePo4 is Lithium Iron Phosphate; it's fairly compatible with SLA voltage range and used as "drop in" replacements for that type of battery in RV, solar, offgrid, etc. You trade off storage density and a need to be above 0C for charging for better safety than typical Li-ion. You can even buy rackmount units that have the BMS breaker, etc all built in.
So, my thinking is you make sure you use correctly constructed and fused cables, use either a properly sized diode or solid state relay for isolation so the UPS doesn't try to charge the big pack, use the correct connector for the external pack, plus a charger for the LiFePo4.
Seems fairly straightforward. If you wanted to it would be easy to add an pure sine inverter for other critical things that could be manually switched over. Personally I also already have a few things that can run "directly" (DC-DC converter) off of the existing batts so I'm not going DC-AC-DC.
Yes, I do have a small generator, but if I could avoid ever needing to mess about with it in the middle of the night ever again...
Plus, even inverter generators have an efficiency floor, and for longer outages need downtime (unless you spend $$$) and need refueling, and even with CO detectors in the house and running it outside as far as I can manage, not running it ever at night would be nice.
LiFePo4 is Lithium Iron Phosphate; it's fairly compatible with SLA voltage range and used as "drop in" replacements for that type of battery in RV, solar, offgrid, etc. You trade off storage density and a need to be above 0C for charging for better safety than typical Li-ion. You can even buy rackmount units that have the BMS breaker, etc all built in.
So, my thinking is you make sure you use correctly constructed and fused cables, use either a properly sized diode or solid state relay for isolation so the UPS doesn't try to charge the big pack, use the correct connector for the external pack, plus a charger for the LiFePo4.
Seems fairly straightforward. If you wanted to it would be easy to add an pure sine inverter for other critical things that could be manually switched over. Personally I also already have a few things that can run "directly" (DC-DC converter) off of the existing batts so I'm not going DC-AC-DC.
Yes, I do have a small generator, but if I could avoid ever needing to mess about with it in the middle of the night ever again...
Plus, even inverter generators have an efficiency floor, and for longer outages need downtime (unless you spend $$$) and need refueling, and even with CO detectors in the house and running it outside as far as I can manage, not running it ever at night would be nice.