Engineering notes
UPS batteries: the same VA is not the same pack
If the internals are fine, do not buy a new UPS because the batteries are old. The pack must match string voltage and the connector. A wrong string faults.
The plant room says “the UPS is dead”. Measure: the inverter is alive, the batteries are old, runtime is tens of seconds. Someone buys a new 3 kVA because it “fits the rack”. You spend a machine; the old unit still needs packs if you keep it. Makers give a pack code, a string voltage (48 V, 72 V), a connector — not loose 12 V blocks jumpered on site.
Flyer runtime is a light load. Read the curve at the real watts. External battery modules are their own schedule line, not inside the UPS price. When you replace: date the packs, do not mix years.