How to interpret Battery Voltage reading vs. battery life

[Trevor loves holden.]

Fluctuations in battery voltage under load are normal and recoverable. Pronounced drops not under load or before starting and during running are not. Maybe have your alternator checked out before finger-poking the battery. Just as a passing mention, I and others were amazed that the battery in my much-travelled (now traded off) VZ lasted all of 8 years, finally showing some ill health in May this year when it was replaced.

Depends on how long you last started it and how much charge was lost in the battery while sitting for a length of time, If the car was sitting for 8hr while at work and not holding charge then the bcm will give it the full 14.8v, if you just stopped for 15min then your battery is most likely almost at full capacity so the bcm will only charge it at a lower voltage. Only real way is a load test while starting as voltage isn't going to tell you to much until it has a load on it, of cause it will give you a guide as how flat it is . Oh if your idling and turn your lights on of cause its going to drop as any load does give it a rev if it doesn't pick up then your alternator is on the blink.

 

[Holden17]

Depends on how long you last started it and how much charge was lost in the battery while sitting for a length of time, If the car was sitting for 8hr while at work and not holding charge then the bcm will give it the full 4.8v, if you just stopped for 15min then your battery is most likely almost at full capacity so the bcm will only charge it at a lower voltage. Only real way is a load test while starting as voltage isn't going to tell you to much until it has a load on it, of cause it will give you a guide as how flat it is . Oh if your idling and turn your lights on of cause its going to drop as any load does give it a rev if it doesn't pick up then your alternator is on the blink.

Some of you guys will know a whole lot more about these things than me...but just in case it helps someone else...

In my recent case, what seemed to give the RACQ dude the confidence that the 6yr old battery was worth saving was when he connected an ammeter (I assume?) to the battery terminals in the boot...said he was checking the alternator....at the same time he had the engine running & the posts under the bonnet connected to his heavy duty battery pack. He had already tried to start the car with a more portable pack which he sat in the engine bay but got nothing so then got his much heavier (had to sit it on the ground) battery pack.

Anyway the reading on the alternator increased from about 4 into the late teens within about 3 mins. I asked what figure he was looking for and he said between 30 and 40. Not sure that it got anywhere near this while he was still connected but that reasonable quick recovery into the late teens was apparently sufficient for him to suggest I try charging it rather than spending the $$$ to replace it at this stage.

Others on here will no doubt have the knowledge to fill in any of the gaps or add to this explanation??

 

[Trevor loves holden.]

Ammeter is current flow thru a circuit, so he was probably testing your cable for amps flow rate to make sure there not to much current lose between Alternator and battery so he knows your battery is charging at the correct rate, Voltage is between 2 points.
On the side of your Alternator it will say 40amp or something like that so he was testing the amps at your battery to see how much drop there was between 2 points. The boost pack was put on to get a steady flow rate if your battery was flat.

 

[Geoff6666]

My battery is now 6years old, late 2013 build. I installed a dash-cam about a year ago and it records 24/7.
As the car can sit for a week at times this caused the battery to go flat. (I have since fitted a kit with battery drain protection.) It would not even unlock the doors. I put it on a charger for about an hour and it was then able to start the car.
I thought that might be the end of the battery but it has been going okay ever since. Also it has to crank for about 4 seconds to start when cold because I am running on United E85. Never had the problem with Caltex E-Flex but I can't get that now.
On a similar note does anyone know if you can clutch-start these cars? I haven't tried it but with a push-button start you can turn on the ignition by holding the button in for about 10 seconds. Will it then start if you push it like we did in the "olden days"?

 

[Big Red VF-SII Go-kart]

On a similar note does anyone know if you can clutch-start these cars? I haven't tried it but with a push-button start you can turn on the ignition by holding the button in for about 10 seconds. Will it then start if you push it like we did in the "olden days"?

What is a "clutch-start"?
Be it noted though that the VF is one-touch start; it does not need to have the button continuously pushed to start the car. Just press, release and it will start after typically 2 cranks.

 

[stooge]

Will it then start if you push it like we did in the "olden days"?

that raises a good question and i guess it would take someone to actually test that but you would assume that with it in ignition on mode after pressing and holding the button it would fire and detect the engine running when you clutch start it.
the question will be will the injectors inject the fuel needed and will the spark plugs fire to get it started.
in the old days with carburetors you could just give it a few pumps and the fuel would be there and the plugs worked on a mechanical system so they would fire but with the vf the ecu will need to open the injectors and fire the plugs.

 

[Skylarking]

How to interpret Battery Voltage reading vs. battery life?

Short answer; well to be honest you can’t.

Long answer; As @chrisp stated in this thread, the VF uses a type of lead-acid battery containing a calcium additive which are prone to suffering acid stratification. To solve such acid stratification, the charging system is designed to periodically ‘gas’ the battery to remix the acid. It does this by raising the battery voltage to a gassing point. This is why you will occasionally see battery voltages up to 15.5V

Further to the above, the BMC works with the ECU, Instrument cluster and Battery current sensor to control the Generator. The BCM thus manages the state of battery charge via a charging algorithm which has 6 charging modes (according to the workshop manual).

With each of these modes, different voltages are seen on the DIC but we simply don’t know which mode we are in at any time. As such, it’s impossible to accurately use the battery voltage you see within the vehicle DIC to determine battery or alternator health (in the old days seeing 15+ volts would have been a concern).

If you suspect a battery issues, and VF’s must use the factory recommended sealed calcium battery (with vent tube) to work with the vehicle’s charging system, your best bet is to first take the battery out of the vehicle. Then, out of the vehicle, you can try charging the battery with one of the new smart chargers on the market that works with calcium batteries and has a recovery (sulphation) mode amongst other modes. Finally you can and should get a load test of the fully charged battery. That will give you a clear idea if the battery is ok or not.

Since you’ve had an issue with the battery going flat, I’d do a last sanity test by leaving the battery out of the car for 24 or 48 hours and periodically checking it’s voltage. Plot a Volt vrs time curve and you’d soon enough see if there is any issue.

If the battery seems to have recover after off car charging and tests OK, you can install it back into your vehicle. Many have stated on the VF forum that a locked car should be able to be parked for at least 6 weeks without start issues.

Should you still have issues with the battery going flat, you’d need to get the vehicle charge system checked, particularly the battery current sensor (serviceable = replicable part). This sensor is critical in measures amps going into and out of the battery and is uses this to estimate the battery Ah capacity and via other parameters determine which mode to charge with.

It’s not like the old days of an battery, an alternator and a volt gauge...

 

[Geoff6666]

What is a "clutch-start"

A clutch start is where you get the engine to rotate without using the starter motor.
It can be pushed or allowed to roll down a hill. Then, with the ignition on, you put the car in gear. When you release the clutch the momentum of the car will cause the engine to rotate which will make it go.
I don't know if the ECU will allow the fuel and spark to operate in this situation.
I'll have to give it a try.
It can't be done with most automatics as the torque converter needs to be operating to select gears.

 

[chrisp]

Battery life is usually measured in two ways. Firstly in terms of its capacity (Ah), the usual ‘end of life’ is 80% of it’s stated capacity. The other useful way of measuring battery life is it’s internal resistance. The ‘end of life’ measure is when the internal resistance doubles.

Both these measures are difficult to do accurately in the field. and the conditions under which the measurements are done also need to be controlled in order for the measurements to be meaningful.

For capacity measurements, the battery needs to be fully recharged under the conditions stated by the manufacturer and then discharged at a controlled rate until flat (typically 10.2V) while the current and time are measured/recorded. This is impractical to do in the field.

Internal resistance measurements are a bit easier to do in the field as there are portable instruments that will measure the internal resistance - but it’s a lot more specialised than a multimeter. The instrument places a pulse-load on the battery and measures the delta-V and delta-I to calculate the internal resistance. However, to get a meaningful internal resistance measurement, the battery needs to be in a defined known state (usually fully charged and room temperature). Therefore, even with the right equipment, it is easily possible to get erroneous measurements if the battery is in the wrong state as the internal resistance also varies with the state-of-charge of the battery. i.e. a flat battery will also exhibit a high internal resistance.

There is some good news - most cars can operate quite happily with a battery that has technically failed (i.e. a battery that is below 80% capacity) as a car only uses about 1Ah to start (whereas a new fully charged battery has a capacity of about 60Ah ~ 80Ah). So, a battery that has trouble starting a car has well and truely ‘failed’ (below 80% capacity) - this is assuming that the car’s electrical system is in good working order.

I usually replace my battery when it starts to show signs of struggling to start the car - particularly in cold weather.

 

[stooge]

VF’s must use the factory recommended sealed calcium battery (with vent tube) to work with the vehicle’s charging system

No they dont, the whole system runs perfectly fine using aftermarket batteries like the din65lh.
Both the ve and vf all variants work just fine with them.

https://www.centurybatteries.com.au/resources/battery-finder/product/din65lh mf/70472