If you pick up consumer-grade UPS units during closeout sales, they cost little more than replacing the batteries in older units… so we now have a new UPS replacing an old Waber box.
Just for completeness, I pulled the 25 A internal fuses:
And then measured the remaining battery capacity:
The pair of sealed lead-acid batteries claim 5 Ah each, so the 6 A load far exceeds the usual C/20 SLA test current. The fact that the better one hit 1.6 Ah under that load says it’s in surprisingly good shape.
In fact, the label I put on that battery in January 2008 says it hit 1.4 Ah at 2.5 A, so it’s doing much better than you’d expect.
However, the UPS claims to support 650 VA = 450 W at 0.7 power factor. The batteries must supply the real power while the inverter drives the reactive load; giving Waber the benefit of the doubt at 90% efficiency says the batteries must provide 500 W = 21 A at 24 V under full load.
Soooo, a 6 A test load doesn’t actually put the screws to them.