How do I test UPS batteries without dropping the load?

Impedance or conductance testing is performed on a live circuit and is the routine tool, fast, non-invasive, and reliable for detecting open cells, dry-out and connection degradation, provided you have a baseline from installation. What it does not do is measure capacity. A timed discharge test does, and requires either a second string, a maintenance bypass, or a portable load bank with the UPS on bypass. The pragmatic regime most Australian asset owners land on is impedance trending at every scheduled visit, with a discharge test at a defined interval or when the trend crosses a threshold. AS 2676 is the reference for the obligations.