I suspect most people are unaware of this important fact.
Battery voltage too low?
- Thread starter RichardZ
- Start date
I suspect most people are unaware of this important fact.
Your going to need a Fluke or better meter that has been calibrated to really be able to use voltage to determine state of charge.
Load test is much better.
Full charge resting voltage will vary among batteries pulled of same assembly line on the same date., so applying one chart as being accurate for each and every 12v battery, is unwise.
The chart is an excellent way of showing just how much less voltage can be expected at low battery temperatures, but anyone who does indeed have a calibrated fluke, takes a reading and declares the battery to be xx.xxx% charged is delusional . +/- 10% removes that delusion, and AGMs tend to have much higher full charge resting voltages
Voltage as an indicator of state of charge should be a general guide ONLY, and only when the battery has not seen any loads or charging sources in many hours, and newer batteries can retain surface charge voltage for many days. Those who claim one can remove surface charge by x load for x period of time, well both those variables change with the size age and temperature of the battery
If one wants precision and accuracy, they should insure a battery has at least one cycle, is fully charged, then take specific gravity readings on all the cells, if possible, note the battery temperature and the voltage at 6 hours, 12 hours 24 hours off the charging source.
new batteries behave weirdly. If put on a top charge on purchase, their amperage will not taper to expected levels as they will if discharged to 80% then recharged, and voltage retained on that initial use, will not be as high s it will be as high as it will had it been drained to 80% or less then promptly and fully charged.
The simple load test is much easier to give an indication of state of health, and charge, but each and every load tester also applies a different load and duration and their voltmeters are hardly precision instruments so while it can be compared to earlier load tests with teh same tool, it cannot be directly compared to the load tester your neighbor has., though additional data is almost always a good thing.
The DIY'er wanting to monitor battery condition would have a 3 wire digital voltmeter with ground and V sense leads right to battery terminals, and watch it closely each and every engine start. They only take readings 2 or 3 times a second so even this will not capture the true minimum voltage during engine cranking, but they will show the obvious trend with battery temperature, engine temperature and battery age.
One can watch a new battery start a cold engine and maintain 11.9v+, and near the end of life it will be in the mid 8's and barely be able to start in the high 7's.
Whille these can be calibrated, the adjustment potentiometer is so sensitive that 0.01 degrees of rotation is equivalent of 0.02 v of change, and one must exert no downward pressure on the mini potentiometer. I've found they line up close enough to my DMM out of the box that further calibration, considering mine is no calibrrated fluke, is good enough and more than good enough for comparison to itself in future readings.
Overnight cold engine starts will have voltage drop considerably more than a warm engine restart, for all the obvious reasons, and such a tool will reveal just how much and take all the suprise out of an aging battery and when to replace it.
A Load tester is trying to replicate the load of a starter motor, but you already have the starter motor, so all you need is a voltmeter and the wherewithall to wire it up correctly, watch it when you turn the key or press the button. It will also show you how insane your vehicle's voltage regulation is, and newer cars will likely have it bouncing around from 12.4 to 15v in normal driving while ti tries to eeek out a few hundredths of a % of extra fuel economy.
The chart is an excellent way of showing just how much less voltage can be expected at low battery temperatures, but anyone who does indeed have a calibrated fluke, takes a reading and declares the battery to be xx.xxx% charged is delusional . +/- 10% removes that delusion, and AGMs tend to have much higher full charge resting voltages
Voltage as an indicator of state of charge should be a general guide ONLY, and only when the battery has not seen any loads or charging sources in many hours, and newer batteries can retain surface charge voltage for many days. Those who claim one can remove surface charge by x load for x period of time, well both those variables change with the size age and temperature of the battery
If one wants precision and accuracy, they should insure a battery has at least one cycle, is fully charged, then take specific gravity readings on all the cells, if possible, note the battery temperature and the voltage at 6 hours, 12 hours 24 hours off the charging source.
new batteries behave weirdly. If put on a top charge on purchase, their amperage will not taper to expected levels as they will if discharged to 80% then recharged, and voltage retained on that initial use, will not be as high s it will be as high as it will had it been drained to 80% or less then promptly and fully charged.
The simple load test is much easier to give an indication of state of health, and charge, but each and every load tester also applies a different load and duration and their voltmeters are hardly precision instruments so while it can be compared to earlier load tests with teh same tool, it cannot be directly compared to the load tester your neighbor has., though additional data is almost always a good thing.
The DIY'er wanting to monitor battery condition would have a 3 wire digital voltmeter with ground and V sense leads right to battery terminals, and watch it closely each and every engine start. They only take readings 2 or 3 times a second so even this will not capture the true minimum voltage during engine cranking, but they will show the obvious trend with battery temperature, engine temperature and battery age.
One can watch a new battery start a cold engine and maintain 11.9v+, and near the end of life it will be in the mid 8's and barely be able to start in the high 7's.
Whille these can be calibrated, the adjustment potentiometer is so sensitive that 0.01 degrees of rotation is equivalent of 0.02 v of change, and one must exert no downward pressure on the mini potentiometer. I've found they line up close enough to my DMM out of the box that further calibration, considering mine is no calibrrated fluke, is good enough and more than good enough for comparison to itself in future readings.
Overnight cold engine starts will have voltage drop considerably more than a warm engine restart, for all the obvious reasons, and such a tool will reveal just how much and take all the suprise out of an aging battery and when to replace it.
A Load tester is trying to replicate the load of a starter motor, but you already have the starter motor, so all you need is a voltmeter and the wherewithall to wire it up correctly, watch it when you turn the key or press the button. It will also show you how insane your vehicle's voltage regulation is, and newer cars will likely have it bouncing around from 12.4 to 15v in normal driving while ti tries to eeek out a few hundredths of a % of extra fuel economy.
gathermewool
Site Donor 2023
Man, lots of misinformation here!
As others have correctly stated:
1. The battery needs to be charged and load-tested (it was and shows life left)
2. The battery was in a reduced state of charge based on the information we initially had (thanks for the chart, bbhero)
What others have incorrectly stated:
1. The battery is toast and needs to be replaced immediately
- As you can tell, I don't subscribe to the 4-5 years and done philosophy, especially for a northern battery in the trunk
2. You need an expensive Fluke to obtain an accurate voltage reading
- My cheap Chinese-made DMM's provide the same indications as my Fluke. That's not to say I trust their readings more than my Fluke; I'm simply stating that cheap DMM's are adequate for something like a 12VDC battery volt check.
3. The voltage drop across the leads is substantial enough to change the voltage indicated on the DMM
-You can measure this yourself...
That's just a few that I picked up, mostly on the first page, some throughout.
/
I believe the OP is OK, mostly based on the fact that he already stated he has a Li-Po jump pack. So, barring a shorted plate, he's good to go if the battery simply fails to start one day due to too low of CCA. If that happens, he can go get a new battery. Who knows, that might be five more years from now!
Now that the battery is fully charged, what's the level of the acid in your batteries? Do your batteries have removable caps to check?
As others have correctly stated:
1. The battery needs to be charged and load-tested (it was and shows life left)
2. The battery was in a reduced state of charge based on the information we initially had (thanks for the chart, bbhero)
What others have incorrectly stated:
1. The battery is toast and needs to be replaced immediately
- As you can tell, I don't subscribe to the 4-5 years and done philosophy, especially for a northern battery in the trunk
2. You need an expensive Fluke to obtain an accurate voltage reading
- My cheap Chinese-made DMM's provide the same indications as my Fluke. That's not to say I trust their readings more than my Fluke; I'm simply stating that cheap DMM's are adequate for something like a 12VDC battery volt check.
3. The voltage drop across the leads is substantial enough to change the voltage indicated on the DMM
-You can measure this yourself...
That's just a few that I picked up, mostly on the first page, some throughout.
/
I believe the OP is OK, mostly based on the fact that he already stated he has a Li-Po jump pack. So, barring a shorted plate, he's good to go if the battery simply fails to start one day due to too low of CCA. If that happens, he can go get a new battery. Who knows, that might be five more years from now!
Now that the battery is fully charged, what's the level of the acid in your batteries? Do your batteries have removable caps to check?
Last edited:
Still a helpful guide.... Nothing is one hundred percent in regards to batteries.... That is obvious. But that chart is helpful to a degree. Good bad or indifferent.
A 16 hour constant current charge is known to rejuvinate deeply discharged AGM batteries.
Charge the battery at 1/10th the C1 rate. If your battery is 30 amp hours, charge it at a constant current of 3 amps for 16 hours. Taking a break at the 8 hour point is often a good idea.
A 12V battery will generally end up with 18V at the charger terminals to push the current through at 10% of C1.
Charge the battery at 1/10th the C1 rate. If your battery is 30 amp hours, charge it at a constant current of 3 amps for 16 hours. Taking a break at the 8 hour point is often a good idea.
A 12V battery will generally end up with 18V at the charger terminals to push the current through at 10% of C1.
Cujet, what kind of power supply do you use to push a constant current like that?
The OP lives in the Southeast and he owns a 4Runner which has it's battery mounted in the engine compartment. 5 years is a good lifespan for a battery in the engine compartment of a hot climate vehicle, and the OP's battery might actually be 6 years old. I never get more than 4-5 years out of a battery here in Texas, regardless of who manufactured it or how expensive it is. My wife's Honda CR-V goes through batteries every 3 years, like clockwork. I made the mistake once of trying to milk some life out of a battery that I knew was on it's last legs and lost a starter because of it. That was an expensive lesson. A weak battery can also take out an alternator. Now when a conductance tester says "replace", I just replace it.
To the OP, my advice stands, replace the battery. You have gotten your money's worth out of it.
Last edited:
Just about any bench top power supply will do it.
