Better yet, do like Blue said, and check the actual battery voltage when you see the drop. If something is sucking down a charged Optima that low, even those 0 gauge cables should be getting warm. So I doubt you will see a drop there.
But, instead of doing a voltage drop test, you need to do a voltage drop test........
I know that does not make any sense, but I am coming off the Flu and my brain is slow.
Measuring from positive to negative at different points will show a problem, but then you have to figure out which side its on.
Technically that would be a low voltage test. Aha! figured it out! You want to do a voltage drop test instead of a low voltage test.
OK, once you are sure the battery is holding its own, you need to do a voltage drop test. That test shows where the problem is. It works off the fact that two points in a circuit that should have pretty much zero resistance will have the same voltage. I usually do it with the engine off and all loads on.
I turn the engine off, turn on all the lights, fan on high, anything that can load the system.
Then you set the voltmeter on a low scale, such as 2 volts and start measuring between connected points looking for a voltage difference.
For instance, with a top post battery, measure from the post its self to the clamp. Since they are supposed to be a nice clean connection, there should not be any voltage difference. A dirty or corroded connection will show a voltage difference because some voltage is lost in the resistance as heat.
I start at the battery post, and leave the probe attached there and work my way down the line.
Positive post to positive clamp, then post to the wire inside the insulation in case the wire connection inside the clamp is bad. Then post to what ever the wire hooks to. When you see a volt or two loss, or more, that is usually the problem.
Of course do the negative side too. In this case, you might want to start on that side.
If its affecting the charging circuit too, you may have to do the checks with the engine running. For instance checking from the negative post to the housing of the alternator and from the positive post to the output stud on the alternator.
But it should not be the alternator its self, because that optima should not let the volts drop to 10.
Having said that, I actually had an Optima go bad on my the other day. First one ever. Less than 6 months old, no hard knocks or damage, just suddenly started getting sluggish about cranking. Battery would charge right up, but would drop voltage while cranking.
Took it back, they gave me a brand new one, no questions, no charge. I just saw that when I typed it...........
I knew the owner of that shop well, and he told me that he had seen a couple come back recently, but only one or two. Probably a factory defect.
But not any since.
Just notices K5wrench suggested the voltage drop first, oh well, I just elaborated on his idea.......
