Can a battery be tested while flat?

[carmanmemoranda]

They usually have a smart charge system on the car, therefore needing that type of battery.

But I still don't think resting voltage of 13.0 volts is good.

It just doesn't sound right, I've never known any battery to sit after resting at that voltage

Out of interest what car is it fitted to?

 

[Renault4]

It is currently at 13.49 V and it is over 19 hrs since last charge.
Temp will be about 10℃.
The car is a 2008 Golf 1.9TDI.

 

[carmanmemoranda]

Battery doesn't sound good to me then.

Impossible to say without a proper test, but even brand new fully healthy battery will only sit around 12.6 to 12.8

 

[Stivino]

Are you sure your voltmeter is accurate, because it shouldn't be reading 13.49V.

 

[Renault4]

Are you sure your voltmeter is accurate, because it shouldn't be reading 13.49V.

That meter currently says 13.48V.
Another meter I have says 13.47V
A charger I have which gives a reading when connected to battery (before being plugged in) says 13.5V

 

[Mottie]

Sounds underpowered to me for a seven cell battery….

 

[Renault4]

They usually have a smart charge system on the car, therefore needing that type of battery.

Can you expand on that?
Is the smart charge system part of a normal alternator or is it only on the cars which need to have battery information coded into them when a new battery is installed? Would a 2008 Golf have a "smart charge system"?
OR
Would all new alternators now be able to correctly charge both an ordinary lead acid battery AND a calcium battery?

Do the claims that some cars can't properly charge a calcium battery apply only to some sub categories of calcium batteries (calcium-calcium??silver-calcium??) and not to lead-calcium which seems to be very common now, and so normal that it is not always even mentioned on the battery?

 

[carmanmemoranda]

As a general guide it is usually found on vehicles with stop start systems.

The battery works harder and needs a more often charge when operating in such situations. Less so when on motorway type driving, hence the smart charging.

Different types (manufacturers) use different types of smart charging. But they all need the correct battery type fitted

Don't know what your car is or has, system wise.

But the big question to me is why the battery is stting at 13.5 volts.

Something isn't adding up

 

[Renault4]

But the big question to me is why the battery is stting at 13.5 volts.

Something isn't adding up

I tried to do a capacity test - discharging at C/8.9 down to 11.9V which should be (?) close to 50% capacity - see attached results.
It is difficult to know what is 50% capacity though when starting voltage is so high.
And looking at the voltage 15 mins after recover - 12.3v and rising, it looks as if there was well over 50% left although again the high fully charged voltage creates some uncertainty about interpreting that figure.

[Caveat - I don't know how accurate clamp meter used to measure discharge current is - will aim to check that, and I don't know what normal 50-% capacity would normally be achievable from a 13 month old, 62Ah battery]

 

[carmanmemoranda]

Maybe try something like a headlamp bulb to drain the battery until the voltage drops to around 10v, then just let it stand, see what it recovery to and how long it takes. It should take a coupke minutes or so to drain it that far

I'm suspicious of the battery, the figures don't add up

Did it recover to over 13v again

 

[Renault4]

Maybe try something like a headlamp bulb to drain the battery until the voltage drops to around 10v, then just let it stand, see what it recovery to and how long it takes. It should take a coupke minutes or so to drain it that far

I'm suspicious of the battery, the figures don't add up

Did it recover to over 13v again

OK - I've discharged it with a headlamp bulb. That gives a current of about 5A which is about C/12.4. I don't want to take it right down to 10V as I gather that would be harmful. At C/12.4, the battery would be totally discharged at 10V - according to the chart at:
https://louwrentius.com/a-practical-understanding-of-lead-acid-batteries.html
I've taken it down to just past 11.7V (and got 27Ah) which, according to the chart, should equate to 25% capacity.

If that chart applies, it looks like battery capacity is down from the nominal 62AH to about 36AH.

BUT, after 45 mins the battery had recovered to 12.09V (and probably still rising) which according to another chart, equates to over 50% state of charge, but that seems unlikely.

 

[carmanmemoranda]

You do understand nobody can tell you if your battery is good bad or other over the Internet?

What voltage is the battery now its rested for x? Hours?

Then recharge it fully and check voltage over the next 4 hours as it rests.

 

[robinbanks]

as it takes a full charge and holds a good voltage

Doesn't mean anything, I'm afraid; your battery might register as full on your charger and show 12.6, but when you attempt to start a car with it all you get is a brrr-click

The high charge voltage needed means that it is impossible to trickle charge

Trickling is a function of amps , not volts

I also doubt you can draw any guaranteed conclusions as to what testing was performed or the state of charge at test time, purely by measuring the battery voltage when you got home..

 

[Harry Bloomfield]

The reason for my question is that I'd like to know if the claim that it can be tested and condemned while flat is also fake.
12.6V is the threshold below which a 12v lead acid battery should be charged. It should be well above that for a good while after charging (unless under load).

Modern battery testers, don't work on the same principles as the older, heavy discharge ones. Modern ones just take a minimal current, to determine the volts drop, and internal resistance of the battery. I would suggest that cannot be done with the battery flat, but it does need some level of charge in it, but unlike an old fashioned tester - it doesn't need to have a full charge.

I possess such a tester, microprocessor controlled - you start by choosing the battery type, and capacity into it, after connecting it, then it runs the test on the battery, finally displaying the CCA, internal resistance, and remaining capacity. You can also start the car, and have it check the alternator charge.

 

[Renault4]

Trickling is a function of amps , not volts

I think the point being made was that if a calcium battery needs a higher voltage for a full charge, a normal float charge function which keeps a conventional battery fully charged, would not do that with a calcium battery.

I also doubt you can draw any guaranteed conclusions as to what testing was performed or the state of charge at test time, purely by measuring the battery voltage when you got home..

I was told it was tested while flat.