Load testing battery and alternator in truck??

I am having a few issues with my Chevy truck, and decided it was time to check on the battery and alternator. Went to Autozone for load test on both, and the counter guy brought out a hand held tester, checked both and said they tested good. I had them test a vehicle there before, but then they used a roll out cart that had a lot more equipment, and the test for the alternator called for engine to be run up to 2000 rpm's and held there for a few seconds to get a reading. The hand held tester was only used while truck idled.

Can a battery and alternator be accurately tested this way? I am not sure I trust the results when the test is only run at idle, and doesn't read the electrical system at operating conditions. The alternator showed it was putting out about 36 amps, and it is supposed to be a 100 amp alternator. When I asked the guy about the difference, he said it was charging and the reading was normal, even though the engine was only at idle. I just don't see how an alternator can be tested without the engine being up to normal operating rpms.

Am I wrong about the testing method? I want to keep my electrical system in working order as this is my daily driver and I don't want to end up broke down on the side of the road, or get off from work to find a dead battery with no way to get it going. I would appreciate your thoughts and opinions on this, and if anyone has suggestions for a better method to test my electrical system I would be glad to here about it.

Thanks in advance.

Sounds like the dieode in the alt is failing. Going from memory it has 3 wires [or legs] when it starts to fail it will burn the leg. Each one takes 1/3 of the total output. So if you have 36 amps sounds like you have 2 legs burned. I just went thru the same thing on my ford,had it checked 4 times and they said it was good but still wouldn't produce 12.6 v . Replaced the alt and ta da it charges. I'm with you on being very leery of the new testing equip and the $5 phr guy working it.

Hello big 86,
You did not say what those ISSUES are.
A battery is tested when fully charged.
It is loaded with a (Load Tester) at 1/2 the CCA
of its capacity.
A 600 CCA amp battery would be LOADED at 300 amps.
To pass as a good battery, the LOAD is held for 15 seconds. Voltage should be at least 9.6 volts at 80 degrees F.
The alternator is tested at least with the engine at 2000 RPM'S The load in amps is usually 80% of the max alternator output. In other words if it put out 80 amps at 2000, it is a good alternator. An alternator will charge 1/3 its capacity at idle, so your 100 amp alternator output of 36 amps at idle is about right.
Guido.

My local CNH dealer used a small hand held digital device to test the battery out of my Kubota this past year. The connection leads and clips were light duty so there is no possible way that the device could have put a noticeable load on the battery. An electrical engineer, I cannot believe that an automotive type battery can be properly tested with such a device.

That said, the battery tested weak and it was, as I suspected.

I believe in the good old fashioned carbon pile load test method which requires a tester of significant size and weight connected to the battery with heavy gage cables and clamps.

In circuit testing of the alternator, however, can be satisfactorily accomplished electronically by measuring output voltage, which doew not require an instrument of large size and mass.

Dean

I have and use the carbon pile load tester. It is actually the same one that was at the dealership when I started working there in 1958. It works great to load test and also load battery to test alternator max out put and of course voltage under all conditions.
Now days there are different ways to test a battery integrity. I read up on it some but a good accurate tester will cost you well over 700 dollars if I remember right. Supposed to be able to tell if battery is good all ways even if dead. I don't know if I believe all that but it is the new way of doing things I guess.