AndySpill
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- First Name
- Andy
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- Oct 24, 2023
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- Pittsburgh
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- 2018 JL Sahara
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- #1
Hook a multimeter like this one, https://www.harborfreight.com/elect...ters/7-function-digital-multimeter-59434.html or hundreds of others like it, to the terminals of your battery and you will get a reading of that battery's voltage.
Actually, in dual AGM battery JLs this is not true. In such vehicles the actions described above (at least while the vehicle is parked--which is a time when both batteries are connected in parallel) will give you a composite reading of the voltage of both batteries, which is even more useless than the point I'm about to make. But before I do make my point, so we're all clear, two black factory cables lead to the negative post of the main battery on dual AGM (Absorbent Glass Mat: a fancy lead acid battery) battery JLs (i.e. not 4xe models, not E torq models, which lack dual AGM batteries.) One of those cables has as its other end the body ground located on the passenger's front quarter panel just under the hood. It's this body ground cable you leave untouched.
The other black cable has as its distal end the negative terminal of the ESS/Aux battery. You must first temporarily disconnect this cable before putting your tester on the main battery's terminals in order to get accurate measurements of just the main battery., regardless of which tester you use: multimeter (volts) or load tester.
Switch the tester's (again, and from this point on, that means multimeter or load tester) negative end off the main battery's negative terminal and on to the dangle cable, with no other changes, and it will give you a reading of just the ESS/Aux battery. Yes, I know, your tester's positive is still on the main battery. But the only circuit you've formed doing this is through solely the ESS/Aux battery, and as such, your meter's reading will only be of the ESS/Aux battery.
Don't forget to reattach that cable--unless your running deliberately with one battery and turned of ESS and yanked Fuse 42---a story for many other threads. If you simple take your tester to the main battery's terminals, without this cable disconnection step, it is possible that one battery could compensate for the other and the readings you get could either fail to detect a problem, or reveal one but give you no clues as to which, or both battery has issues.
(Before continuing let a take a quick dive into how those batteries are connected, which is in parallel (not serial). Parallel connections pair the positives of one battery to the positives of another, same for the negatives. Such connections should be with batteries of the same type (i.e. AGM) that when fully charged have the same voltage. Batteries connected in parallel help to increase the amps, which get combined, while keeping voltage roughly constant. In actuality voltage will equalize between the batteries.
Battery purists would find the parallel connection of the dissimilar sized AGM batteries of the dual AGM battery JL to be "all sorts of wrong," and a source of some of the ESS system's problems: a story, again, for another thread.
Serial connections daisy chain the positives of one battery to the negatives of another and serve to increase voltage, not amperage. They are not relevant here.
It is not uncommon for solar installers to connect batteries in parallel, to form yet one bigger composite battery, repeating that with a whole other set of batteries, and then take those two composite batteries and hook them up serially or parallelly.)
And these same cable disconnect steps work whether your using a multimeter (i.e. voltage tester) or load tester, but still doesn't get me to my original point: why we load test (each battery independently).
Maybe it's best to approach the answer by recalling that watts, which measures energy--just like its "friends" joules or British Thermal Units (BTUs) that also measure energy--is the result of multiplying volts and amps...and sometimes we call amps current.
So volts, which your multimeter tests, is only, sort of, half the story. Certainly if your multimeter correctly reads, say, 4 Volts on your vehicle battery you can correctly assume that there are problems. But in the converse, an adequate voltage reading of say 12.7 volts doesn't mean that your battery is good. For example, the second you hook an appliance (an electrical device that does some work for you in exchange for accepting watts, be it a car stereo, off roading lights, a winch, etc,) up to that battery it may, despite the adequate voltage reading, be unable to deliver amps, i.e. current, or do so for adequate durations of time: the true test of a battery's ability to deliver power.
BTW: for newcomers, that "12 Volt" battery you have. Well at 12 actually volts its on its last legs. Around 12.7 volts is more like what we'd expect.
A load tester tests the ability over time for a battery to deliver watts, i.e. power, energy, pick your favorite word. In essence it tests "that a battery needs to do" (that and accept power back from the alternator.)
If a metaphor is required I'll try the one I did on my teenager:
"See that bodybuilder on stage. Looks 'great' doesn't he/she? Truth is they're exhausted from lack of sleep, dehydration, caloric restriction, crazy low levels of body fat, and the physical exertion from training (no disrespect intended,) and if I asked them to exert themselves, given that they're practically, just standing there, ready to collapse, I doubt I'd get much out of them.
Well, that's like a test of volts.
Now, focus your attention on that power lifter with the big body, lack of muscle definition, even big belly. Or if you prefer, pay attention to that lean Navy Seal with 14% body fat that can walk on his hands for a mile. Those guys have power. Either a multimeter or load tester would prove them first rate. The power lifter might beat the Seal in arm wrestling but the Seal carries more muscle per body weight, and can probably exert themselves, before collapsing, for longer periods of time."
For more reading:
https://iask.ai/?mode=question&options[detail_level]=detailed&q=why+is+a+multimeter+test+of+a+car+battery+inadequate+and+a+load+test+is+best?
(This clearly is not the last word on this subject nor am I. I warmly welcome critique so I can write it better and/or more accurately.)
Actually, in dual AGM battery JLs this is not true. In such vehicles the actions described above (at least while the vehicle is parked--which is a time when both batteries are connected in parallel) will give you a composite reading of the voltage of both batteries, which is even more useless than the point I'm about to make. But before I do make my point, so we're all clear, two black factory cables lead to the negative post of the main battery on dual AGM (Absorbent Glass Mat: a fancy lead acid battery) battery JLs (i.e. not 4xe models, not E torq models, which lack dual AGM batteries.) One of those cables has as its other end the body ground located on the passenger's front quarter panel just under the hood. It's this body ground cable you leave untouched.
The other black cable has as its distal end the negative terminal of the ESS/Aux battery. You must first temporarily disconnect this cable before putting your tester on the main battery's terminals in order to get accurate measurements of just the main battery., regardless of which tester you use: multimeter (volts) or load tester.
Switch the tester's (again, and from this point on, that means multimeter or load tester) negative end off the main battery's negative terminal and on to the dangle cable, with no other changes, and it will give you a reading of just the ESS/Aux battery. Yes, I know, your tester's positive is still on the main battery. But the only circuit you've formed doing this is through solely the ESS/Aux battery, and as such, your meter's reading will only be of the ESS/Aux battery.
Don't forget to reattach that cable--unless your running deliberately with one battery and turned of ESS and yanked Fuse 42---a story for many other threads. If you simple take your tester to the main battery's terminals, without this cable disconnection step, it is possible that one battery could compensate for the other and the readings you get could either fail to detect a problem, or reveal one but give you no clues as to which, or both battery has issues.
(Before continuing let a take a quick dive into how those batteries are connected, which is in parallel (not serial). Parallel connections pair the positives of one battery to the positives of another, same for the negatives. Such connections should be with batteries of the same type (i.e. AGM) that when fully charged have the same voltage. Batteries connected in parallel help to increase the amps, which get combined, while keeping voltage roughly constant. In actuality voltage will equalize between the batteries.
Battery purists would find the parallel connection of the dissimilar sized AGM batteries of the dual AGM battery JL to be "all sorts of wrong," and a source of some of the ESS system's problems: a story, again, for another thread.
Serial connections daisy chain the positives of one battery to the negatives of another and serve to increase voltage, not amperage. They are not relevant here.
It is not uncommon for solar installers to connect batteries in parallel, to form yet one bigger composite battery, repeating that with a whole other set of batteries, and then take those two composite batteries and hook them up serially or parallelly.)
And these same cable disconnect steps work whether your using a multimeter (i.e. voltage tester) or load tester, but still doesn't get me to my original point: why we load test (each battery independently).
Maybe it's best to approach the answer by recalling that watts, which measures energy--just like its "friends" joules or British Thermal Units (BTUs) that also measure energy--is the result of multiplying volts and amps...and sometimes we call amps current.
So volts, which your multimeter tests, is only, sort of, half the story. Certainly if your multimeter correctly reads, say, 4 Volts on your vehicle battery you can correctly assume that there are problems. But in the converse, an adequate voltage reading of say 12.7 volts doesn't mean that your battery is good. For example, the second you hook an appliance (an electrical device that does some work for you in exchange for accepting watts, be it a car stereo, off roading lights, a winch, etc,) up to that battery it may, despite the adequate voltage reading, be unable to deliver amps, i.e. current, or do so for adequate durations of time: the true test of a battery's ability to deliver power.
BTW: for newcomers, that "12 Volt" battery you have. Well at 12 actually volts its on its last legs. Around 12.7 volts is more like what we'd expect.
A load tester tests the ability over time for a battery to deliver watts, i.e. power, energy, pick your favorite word. In essence it tests "that a battery needs to do" (that and accept power back from the alternator.)
If a metaphor is required I'll try the one I did on my teenager:
"See that bodybuilder on stage. Looks 'great' doesn't he/she? Truth is they're exhausted from lack of sleep, dehydration, caloric restriction, crazy low levels of body fat, and the physical exertion from training (no disrespect intended,) and if I asked them to exert themselves, given that they're practically, just standing there, ready to collapse, I doubt I'd get much out of them.
Well, that's like a test of volts.
Now, focus your attention on that power lifter with the big body, lack of muscle definition, even big belly. Or if you prefer, pay attention to that lean Navy Seal with 14% body fat that can walk on his hands for a mile. Those guys have power. Either a multimeter or load tester would prove them first rate. The power lifter might beat the Seal in arm wrestling but the Seal carries more muscle per body weight, and can probably exert themselves, before collapsing, for longer periods of time."
For more reading:
https://iask.ai/?mode=question&options[detail_level]=detailed&q=why+is+a+multimeter+test+of+a+car+battery+inadequate+and+a+load+test+is+best?
(This clearly is not the last word on this subject nor am I. I warmly welcome critique so I can write it better and/or more accurately.)
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