Regarding UPS

When to change batteries

If it's been >N years since the last change of batteries you must change them. N=1.5 years for normal batteries and 3.5 years for UASA/CSB. For CSB type L N is 5.5 years but we don't use CSB type L.

Smart UPS Run time

Πειραματικά μέτρησα ~11λετπά με φορτίο ~380W και μπαταρίες CSB-HR1234w-f2-12v-9ah (μετά από 6'10" μου εμφάνιζε ότι έχει άλλα 5').

Θεωρητική αυτονομία με την APC μπαταρίες (ή CSB-HR1234w-f2-12v-9ah ή CSB-HRL1234w-12v-9ah)

Understanding Batteries Datasheets

CSB batteries

Datasheet of a 12V 6 cells battery:

_{(Image source: Adapted from the question, originally from CSB HR 1234W datasheet.)}

F.V. (1st column) Final Voltage of each cell

MIN (1st row) Discharge time in MINutes

All other cells display the current you can draw from a battery for a given time(MIN) before the cell voltage drops to the given F.V. value

For example: If you have a 20 A load and don't want to discharge the battery below 10.5 V (6 cells x 1.75V=10.5V) you can keep discharging for something between 17.5 and 23.5 mins.

[source: stackexchange/csb-batteries-... ]

Other Batteries

As an example here's the datasheet of Sunlight SPA 12V battery. In the datasheet you'll find this graph:

Let's say that this is 7Ahr battery and that you want to draw 14A. You'll have to observe the 2C curve (2C means to discharge at 7Ahr*2/h=14A). You'll note that a fresh, fully charged kept at 25°C battery will drop to 9.5V-10V after about 15mins.