about load testing a flooded lead acid battery

I have been asked now and then about how one goes about load testing a flooded lead acid battery. If you do not own a Load Tester (Harbor Freight sells them), then you must improvise, which is certainly OK.  The load testing procedure for a formal Load Tester (or, improvised method) is to FIRST be sure the battery is fully charged....a terminal voltage minimum 14 before disconnecting/turning-off the charger, is a good voltage to use.

Let the battery sit an hour or two.

Connect the load tester and IMMEDIATELY adjust it such that when it will provide a load of 1/2 of the battery's rated CCA. If you do not know that value, then use THREE times the rated ampere-hours (AH) of the battery). Apply the load quickly, monitoring the voltage with a digital meter at the battery terminals. Be careful of the connections, the load is great, and you want the battery terminals, NOT the load tester terminals connection point, to be where the voltmeter is attached. That avoids errors. 15 seconds of the load applied should show, load tester still connected, a minimum of 9.8 volts, if the battery temperature is approximately 20°C.....this is approximately normal pleasant room temperature (68°F).

If you do NOT own a load tester, the normal quickie way of doing this job, and it is perfectly adequate a method, is to remove the fuel or ignition (ground it properly) from the engine so the engine will not start. Charge and then monitor the battery voltage as above. Crank the engine for 10 to 20 measured seconds. At the end of the time period, still cranking, note the voltage....again, 9.8 is the minimum.

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