Automotive cranking LA batteries are designed for short high amperage loads (starter motor etc). The common device for load testing is a carbon pile resistor; basically a stack of carbon/graphite discs that give lower resistance (higher amperage load) the tighter they are squeezed together. Carbon pile load testers are obviously short term test devices. It has been a while since I had occasion to use one, but for a ballpark test of a cranking battery rated at 600 to 800 cold cranking amps, a load of 200 amps for 2 minutes will tell a lot about the health of the battery; the voltage shouldn’t fall below about 10V in those 2 minutes. A discharge that brings any cell below 1.75 may cause loss of capacity, below 1.5 volts per cell may cause permanent irreversible damage.
UPS and other long discharge designed LA batteries are usually rated for a given number of amp hours over a given time. These require longer load test times at much lower current settings. An electronic load bank would probably be able to test the smaller of these batteries and test procedure should be available from the manufacturer.
Another reasonable test is to charge up a battery and then leave it sit for a week disconnected; then read the open circuit voltage. The open circuit voltage depends on the plate chemistry, plate structure, electrolyte density and temperature. 2.25 volts per cell is more or less nominal for a good LA battery open circuit.
One of the best tests for LA batteries is the % of sulfuric acid in the electrolyte; like the old school hydrometers. There are refractometers that are calibrated to measure this that are very accurate and use only a tiny drop of electrolyte. (Less holes in clothes from acid spatter) but using this method on sealed batteries is less than optimal.