Good way to load test battery?

[wirelessF]

According to Deka's PDF on AGM batteries, a way to load test a battery for voltage drop is to use a load tester and set the load to half the CCA of the battery. Less than 9.8v means the battery is damaged. A lot of the handheld carbon pile testers only go up to 130A and those smaller ones that shoot a pulse through the battery to determine CCA and stuff.

I tried a crude way to load test a battery. Hooked up a multimeter to battery, disabled fuel pump and held the key in the start position for 15 seconds. Voltage drop was 11.5V. 1.5Kw starter / 12 volts means its drawing 125 amps. Not really a heavy load but should I put a more heavy load to get accurate voltage drop measurements?

Vehicle tested 02 Chevy Silverado 5.3L, stock starter, Deka Intimidator AGM battery rated at 775 CCA/120 RC

 

[Rick in PA]

I have one of these battery testers, crude but effective:

 

[Corvette Owner]

Almost any place that sells batteries will do a load test for free, take advantage.

 

[cat843]

Carbon pile load tester from HF.

 

[JHZR2]

Carbon pile is the standard. I like to know battery impedance specifically, as then you can calculate voltage drop under any sort of conditions.

IMO though, cranking amps dont correlate well to the starter draw. I like to watch the battery voltage under cranking cold, with as many loads as I can have, on. I think this is a fairly practical way to see if the battery is keeping up.

 

[cat843]

Assuming you do not mind taking the time to charge up the battery, then the carbon pile tester is best. But a place that sells batteries and just wants a quick test, so they use a Midtronics.

 

[cathy]

how do you use these?