DIsconnected new battery, small loss overnight

[mike42]

Hello All

I wonder if some kind person more knowlegable than me can answer this?

Been having some problems with the battery going flat. One test I did was to disconnect the -ve lead at the battery and then hooked up a trickle charger for a few hours. I left it until 12.49V.

Then in the morning I checked and it was 12.44V. I mean shouldn't it hold rock solid at 12.49V ?

Does that mean the battery is already fried?

Sorry if that is a stupid question.

[GreenV8S]

It's perfectly normal for the battery voltage to settle a little after you stop charging it. That tiny voltage change doesn't matter at all.

By the way, the battery should read about 12.6V when it's fully charged so your battery is not fully charged at the moment.

[mike42]

Brilliant - thanks a lot.

I'll fully charge it then monitor it again over perhaps a longer period.

[paul_c123]

Voltage alone won't give a good indication of the state of charge, and definitely won't help find the state of health, of a battery. You want to be using something like a Topdon AB101 battery tester.

[GreenV8S]

paul_c123 said:

Voltage alone won't give a good indication of the state of charge,

There is a predictable relationship between the voltage of a lead acid battery, and the state of charge. That doesn't tell you anything about the battery health or capacity, but does tell you the state of charge. Hence my comment that the battery voltage indicated it is not fully charged.

[mike42]

paul_c123 said:

Voltage alone won't give a good indication of the state of charge, and definitely won't help find the state of health, of a battery. You want to be using something like a Topdon AB101 battery tester.

Thanks. I had a look at that one and correct me if I'm wrong but I don't think it does much a multimeter can't do? FOr example, the crank test could be done with a multimeter with a MIN setting. Parasitic drain test again by any multimeter with a decent amp rating (e.g. 10 amps plus?) .

[mike42]

So I charged it up to what the "smart" charger said was the maximum. It measured 12.90v.

Over the past 24 hours I measured the voltage out of car:

Time Volts
13.17 12.90
18.53 12.87
22.54 12.85

NEXT DAY
13.14 12.82


Battery isn't brand new its about 5 months old. Can I pretty well rule out the battery as being faulty or is that too big a drop?

[paul_c123]

GreenV8S said:

There is a predictable relationship between the voltage of a lead acid battery, and the state of charge. That doesn't tell you anything about the battery health or capacity, but does tell you the state of charge. Hence my comment that the battery voltage indicated it is not fully charged.

Only if the battery is under no load and it is a "rested" voltage. Which can't be assumed or achieved with a battery still connected to a car which has electronic modules which might/might not properly go into "sleep" mode (during which they still draw a small current). And also isn't rested if its recently been charged, because it will have "surface voltage" which will make it not possible to determine a small change in state of charge by voltage measurement.

Edited by paul_c123 on Saturday 5th July 14:36

[paul_c123]

mike42 said:

Thanks. I had a look at that one and correct me if I'm wrong but I don't think it does much a multimeter can't do? FOr example, the crank test could be done with a multimeter with a MIN setting. Parasitic drain test again by any multimeter with a decent amp rating (e.g. 10 amps plus?) .

It is completely different to a multimeter and uses conductance to determine State of Health of a battery.

I often don't even bother with the cranking and charging tests, similar could be done with a multimeter (but you'd need 2 people to properly evaluate cranking, and know how to interpret the results you see).

[Panamax]

GreenV8S said:

There is a predictable relationship between the voltage of a lead acid battery, and the state of charge. That doesn't tell you anything about the battery health or capacity, but does tell you the state of charge. Hence my comment that the battery voltage indicated it is not fully charged.

Yes, this is the best DIY test/assessment. If the battery won't hold at or above 12.5v (stood indoors overnight after charging) it's on its way to knackered.

Battery centres will have a better test, which is a high current load test, mimicking the high load drawn during cranking. Even if the battery can still deliver current the voltage may drop to, say, 9v which isn't enough to run modern car electronics properly. You need a strong battery which can both deliver cranking current and maintain sufficient voltage. Informative video on this link,
https://www.youtube.com/watch?v=J-WekRyyAck

[LunarOne]

You might want to get one of these bluetooth battery monitors. As well as drawing a graph showing your battery charge over time, it also measured voltage during cranking to evaluate the health of the battery. They're cheap and I have one on all of my cars!

https://www.amazon.co.uk/Battery-Monitor-Campervan...

[mike42]

Thanks for the tip Lunar - I'll look into that particularly as my battery is tucked away under the spare wheel in the boot. Can it provide readings when the car is switched off ?

And to the others would my readings seem to indicate its not toast at least ?

Latest reading is:
15.35 12.82V

So no drop since last reading.

Edited by mike42 on Saturday 5th July 15:42

[paul_c123]

LunarOne said:

You might want to get one of these bluetooth battery monitors. As well as drawing a graph showing your battery charge over time, it also measured voltage during cranking to evaluate the health of the battery. They're cheap and I have one on all of my cars!

https://www.amazon.co.uk/Battery-Monitor-Campervan...

What is its current draw?

[wong]

LunarOne said:

You might want to get one of these bluetooth battery monitors. As well as drawing a graph showing your battery charge over time, it also measured voltage during cranking to evaluate the health of the battery. They're cheap and I have one on all of my cars!

https://www.amazon.co.uk/Battery-Monitor-Campervan...

Even cheaper on Aliexpress - https://vi.aliexpress.com/item/1005008234555592.ht...

[mike42]

paul_c123 said:

What is its current draw?

It says 1 ma on the case so presumably not significant and does work with no alternator input? However, I'd have though its draw would vary depending on whether it is activiely being queried by bluetooth?

Any thoughts on my battery dropping a small amount of voltage...? Maybe its normal?

[paul_c123]

It sounds like the first measurement was done shortly after charging and the second measurement was after a period of time disconnected. So, there was surface charge on the first measurement, thus its invalid.

[GreenV8S]

paul_c123 said:

Only if the battery is under no load and it is a "rested" voltage. Which can't be assumed or achieved with a battery still connected to a car which has electronic modules which might/might not properly go into "sleep" mode (during which they still draw a small current). And also isn't rested if its recently been charged, because it will have "surface voltage" which will make it not possible to determine a small change in state of charge by voltage measurement.

I think you're exagerating negligible effects. The original post showed that the battery was disconnected from the vehicle and charging stopped the previous evening, which rules both of those effects out entirely. But even if it had been connected to the vehicle with something drawing tenths of an amp here or there it would not have any significant effect on the battery voltage reading. Under the conditions described the resting battery voltage gives a predictable and reliable indication of the state of charge of the battery.

[mike42]

paul_c123 said:

It sounds like the first measurement was done shortly after charging and the second measurement was after a period of time disconnected. So, there was surface charge on the first measurement, thus its invalid.

I've taken 5 measurements so far (all above).

[ARHarh]

It's probably nothing more than temperature changes. A battery when charging will warm up. A warm battery will push out more electric. The numbers you are seeing are so small just about anything could be the cause.

You really are worrying about nothing.

[E-bmw]

These are brilliant.

https://www.ebay.co.uk/itm/295644935211

I have one on each battery on my motorhome.



Motorhome is currently a few miles away, so ignore "can't connect to bluetooth" message.

Graph is expandable, alarm points can be set, you can carry out cranking tests etc.

Edited by E-bmw on Saturday 5th July 16:52