Dual Battery Volt Meter Readings
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Dual Battery Volt Meter Readings
What should my volt meter be reading on a dual battery 7.3 when I test the battery under the hood?
Yes, I know, ideally each battery should be tested individually, in winter weather ...
Thank you, in advance.
Yes, I know, ideally each battery should be tested individually, in winter weather ...
Thank you, in advance.
Fleet Mechanic
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I usually see about 12.7 to 12.8 on a healthy lead acid battery,a little higher for AGM batteries,fresh off a charger will read much higher until it sits for a day or two,with engine running it will be 14v or higher depending on electrical load.
Fleet Mechanic
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From: Los Angeles, Ca.
The stock set-up is two batteries under the hood, but your post makes it sound like you have one under the hood and another somewhere else...? You mention testing batteries along with your voltmeter question, just know that a voltmeter is nearly useless for testing unless you monitor voltage under load and know what it's supposed to read with a good set of batteries.
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Joined: Oct 2016
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From: Escondido, ca
I'm a little confused with the question.
There is measuring and then there is testing. If you want to measure the voltage using a multi-meter you should be getting around 12.8v. The batteries are not isolated from each other so you should have the same reading on both batteries. If you want to isolate them you would need to disconnect the positive cable from the Driver side battery and read each battery. To do a simple load test in the truck you can have someone crank the engine while measuring with the multi-meter. If the batteries are dropping below 10.8v-11v while cranking you could have an issue and more testing is needed. Note that the Passenger side battery is the starter battery so if you disconnect the driverside battery for test you will not see any voltage drop on it. You can swap batteries around and do the test to isolate them to find which battery is bad.
This all describes a quick in the field type test. The easiest way to test would be to just get a battery load tester or take the batteries out and to a local parts store and have them load test them.
You need to take into account the glow plugs when testing. Best to disable them while doing the crank test.
There is measuring and then there is testing. If you want to measure the voltage using a multi-meter you should be getting around 12.8v. The batteries are not isolated from each other so you should have the same reading on both batteries. If you want to isolate them you would need to disconnect the positive cable from the Driver side battery and read each battery. To do a simple load test in the truck you can have someone crank the engine while measuring with the multi-meter. If the batteries are dropping below 10.8v-11v while cranking you could have an issue and more testing is needed. Note that the Passenger side battery is the starter battery so if you disconnect the driverside battery for test you will not see any voltage drop on it. You can swap batteries around and do the test to isolate them to find which battery is bad.
This all describes a quick in the field type test. The easiest way to test would be to just get a battery load tester or take the batteries out and to a local parts store and have them load test them.
You need to take into account the glow plugs when testing. Best to disable them while doing the crank test.
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Thanks for the quick replies.
'88 E-350 - the stock set up is not two batteries under the hood. The stock set up is one under the hood and one under the passenger side frame rail.
Here is what I am getting with the meter set to 20 Volts:
Not started: 17.56 initially dropping slowly to 17.02 and then staying steady at that. (I had a charger on it the week previously because there was no cranking amps - basically it seemed as if the batteries were very drained and close to being dead (very weak headlamps in the 'on' key position and then when attempting to start very weak turn over attempt without the vehicle starting - after having the charger on it for a while it did start and has not been charged since then).
When started it dropped to 16.8 (tested at load with lights, blowers, 4 ways, radio, door chiming)
After it was turned off the reading went back up to 17.8
I tested the alternator case with the van running. At idle it tested at -0.00 at the front of the case while the back of the alternator casing tested at -0.02.
When the rpms were up to 1500 - 2000 the reading on the back of the alternator went up to 0.09 and 0.10.
Any ideas?
'88 E-350 - the stock set up is not two batteries under the hood. The stock set up is one under the hood and one under the passenger side frame rail.
Here is what I am getting with the meter set to 20 Volts:
Not started: 17.56 initially dropping slowly to 17.02 and then staying steady at that. (I had a charger on it the week previously because there was no cranking amps - basically it seemed as if the batteries were very drained and close to being dead (very weak headlamps in the 'on' key position and then when attempting to start very weak turn over attempt without the vehicle starting - after having the charger on it for a while it did start and has not been charged since then).
When started it dropped to 16.8 (tested at load with lights, blowers, 4 ways, radio, door chiming)
After it was turned off the reading went back up to 17.8
I tested the alternator case with the van running. At idle it tested at -0.00 at the front of the case while the back of the alternator casing tested at -0.02.
When the rpms were up to 1500 - 2000 the reading on the back of the alternator went up to 0.09 and 0.10.
Any ideas?
Last edited by Wmyers; Jan 2, 2020 at 04:40 PM. Reason: added image
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I know what I should be seeing, but considering it is two batteries connected, I was wondering if this was some type of anomaly due to the dual batteries (hence the post's query).
The meter is a GB (Gardner Bender) Digital Multimeter GDT-311 (setting as per above).
The meter is a GB (Gardner Bender) Digital Multimeter GDT-311 (setting as per above).
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FTE Leadership Emeritus
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From: Lake Hartwell, GA
The dual batteries will NOT change the voltage in our systems. The dual batteries changes the amperage in our system. Depending on how a pair (or more) of batteries are wired, they will be in series or parallel and the voltage or amperage will double, not both when looking at a system like ours. Since our system is 12v and not 24v, the batteries are wired in parallel.
Batteries can also be wired in series/parallel, but that is not the case with our system and can get rather confusing.
You should NOT be seeing 17v on a system such as ours...
Batteries can also be wired in series/parallel, but that is not the case with our system and can get rather confusing.
You should NOT be seeing 17v on a system such as ours...
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17+ volts is waaaaay too high. Need to verify.
Try another meter, make sure the internal battery is good. My Triplett will indicate a couple volts high when the internal 9 volt gets weak, caused some head scratching for a minute or two.
If the battery halves are mismatched, when connected in parallel (same as when jump starting btw) then the weak half of the battery will pull the stronger half of the battery voltage down as it charges.
Try another meter, make sure the internal battery is good. My Triplett will indicate a couple volts high when the internal 9 volt gets weak, caused some head scratching for a minute or two.
If the battery halves are mismatched, when connected in parallel (same as when jump starting btw) then the weak half of the battery will pull the stronger half of the battery voltage down as it charges.
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You can see one at 4:27:
Due to the problems, I'm thinking it's not a bad meter (it's been fine until now) but I can hope it may be. I have another I will try it tomorrow.
I did find this for high voltage on another forum (google search):
https://www.yotatech.com/forums/f116...rnator-196151/
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I am getting the feeling no one on here seems to have much knowledge of electrical issues (like this).
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Cant be a voltage reg when he measures the battery with the motor not running and gets 17v. Doesnt make sense whatsoever to be that high.
If you get 17v with the motor running then yes voltage reg is probably stuffed on the alternator. Should only be kicking out 13.5 to maybe 14v at the most.
If you get 17v with the motor running then yes voltage reg is probably stuffed on the alternator. Should only be kicking out 13.5 to maybe 14v at the most.