Am I missing something here? It seems like all UPS models are very clear about the VA, which I understand to be amount of power / watts the device can supply, but this doesn't give any indication of runtime. The Ah (ampere-hours) of the battery should reflect the amount of power stored in the battery, but it isn't even listed in many of models specification sheet.

I'm trying to buy a UPS to power my network rack for as long as possible. The wattage isn't huge, maybe 200 at peak load, but I'd like it to run as long as possible in an outage. Some brands have a "runtime calculator" for each product, but many don't. Is there an easier way to determine runtime? Or am I incorrect in my interpretation of the power units?

Thanks.

I often have to check the health of UPS lead batteries (typically 12V either 9Ah or 7Ah) and replace them before they fail. Most of these UPS do not have a self-test feature (and the ones that have, it doesn't seem very reliable).

My current test method is to just unplug them from AC and leave them running with a load for a few minutes and see if it holds. The ones with an USB connection I can connect to a PC and check how fast their charge drop, etc, but not all have this feature also different brands imply having multiple software installed...

This method takes time and is not very reliable/practical.

Usually these UPS are fairly easy/quick to open and get physical access to the batteries (and unplug them if needed). So I've been thinking about buying one of those battery tester for car batteries (which are usually also lead 12V batteries, just higher capacity). But not sure if they'd work well on 9Ah/7Ah batteries, since they're designed for car batteries which have much higher capacity.

I'm open to any other solution that's not overly expensive...

I've tried using a multimeter, but from what I've read when there's measurable changes in voltage it's already too late and the battery is already in very degraded state...

Changes in internal resistance seem to be a better method to detect signs of upcoming failure in an earlier stage, but as far as I know we're talking about internal resistances in the miliohm range, which might be hard to measure accurately with a typical multimeter (by using the method of measuring the difference in voltage drop with/without a known load and extrapolating the internal resistance from there).

I'm guessing car battery testers use this or similar method to measure internal resistance, but are designed to that purpose and can do it more accurately? Perhaps combining it with other measures?

Anyway looking for advice and other possible options. Thanks.