How long should a 12v Car Battey last?

[Benny5]

I’ve got an August 2016 VW Polo (22K Miles) with its original battery and while there are no obvious signs of failure I don’t want to suffer a sudden breakdown.

Using a multimeter I’ve taken some readings;

1)After standing overnight 12 deg (Garaged) I get 12.17v.
2)Engine running for 2 minutes I get 14.8v.
3)Immediately after switching engine off I get 12.3v.

With greater demands on this over the winter, any suggestions as to the likelihood of this failing in the immediate future.

 

[carmanmemoranda]

I’ve got an August 2016 VW Polo (22K Miles) with its original battery and while there are no obvious signs of failure I don’t want to suffer a sudden breakdown.

Using a multimeter I’ve taken some readings;

1)After standing overnight 12 deg (Garaged) I get 12.17v.
2)Engine running for 2 minutes I get 14.8v.
3)Immediately after switching engine off I get 12.3v.

With greater demands on this over the winter, any suggestions as to the likelihood of this failing in the immediate future.

How long is the bit of string?

Those readings indicate a weak battery, but it might be good enough for another year, or it might fail tonight.

If you want peace of mind, buy a new 1.

 

[Benny5]

Thank you for that.

The battery is not displaying any of the usually failure symptoms, no problem starting, dash light goes out once started and the battery ‘status window’ is black. It’s just I have seen that car batteries generally last for 4-5 years hence the reason for doing the test.

Is it possible to predict if the failure would be total, i.e. won’t take a charge or would a Jump Pack Starter get it running again.?

 

[johnny2007]

Once I removed a 20 year old battery from a VW Polo.
It was a Sainsbury's battery.
Next Bosch singing and dancing battery lasted 5 years and died suddenly without any warning.
Of course 1 month out of warranty.

 

[Harry Bloomfield]

The battery is not displaying any of the usually failure symptoms, no problem starting, dash light goes out once started and the battery ‘status window’ is black.

That alone, suggests you ought to replace it, but add in the 12.17v after standing overnight, and the age...

 

[Benny5]

Really appreciate that.

A cursory look and it suggests Halfords may be my best bet, Yuasa with a 5 year guarantee £155 fitted.

 

[carmanmemoranda]

Thank you for that.

The battery is not displaying any of the usually failure symptoms, no problem starting, dash light goes out once started and the battery ‘status window’ is black. It’s just I have seen that car batteries generally last for 4-5 years hence the reason for doing the test.

Is it possible to predict if the failure would be total, i.e. won’t take a charge or would a Jump Pack Starter get it running again.?

Modern battery failures tend to be total and sudden

You should be able to jump start it

The question is do you want to if you have to

 

[Johntheo5]

I've been driving VWs for over 60 years, and the battery only had to be replaced in one, a 6V ,1963 Beetle, after 6 years, all the others, from new, were in the family as hand downs for 20+ years and I used to replace the battery, purely precautionary, before handing the cars on after 10/12 years. All these cars charged at a constant 14.2/14.4V which meant a 100% SOC. Our present, Jan 2019 Polo has both Stop/Start (only used selectively) and possibly the greatest danger to a very long battery life, a smart charging system which only charges to a max 85% SOC, it charges at 13.3/13.6V normally and up to just short of 15V, 14.6/14.9V, on overrun. Time will tell how long this one lasts. It's now almost 7 years old and I have a cheap < £5 DVM plugged in permanently in the auxiliary power socket. I will post later the VCDS latest data and the first one taken when car/battery about 2 years old.

 

[Johntheo5]

Jan 2019 (petrol) Polo, original 59AH Type EFB Battery

21/10/2025
IDE01834 Battery voltage 12.256 V (Engine Off)
IDE01836 Battery current -4.407 A
IDE01837 Temperature of battery sensor 15 °C
IDE01839 Battery charge level 78 %
IDE01841 Battery internal resistance 7.4 mOhm
IDE01842 Usable battery charge 27 Ah
IDE01843 Battery voltage at rest 12.4 V
IDE01948 Battery internal resistance not normed 6.8 mOhm
IDE07681-MAS06086 Battery total charging throughput-Total re-charge 3480.7 Ah
IDE07681-MAS06087 Battery total charging throughput-Entire energy throughput 3671.1 Ah

14/09/2021
IDE01834 Battery voltage 13.487 V (Engine Idling)
IDE01836 Battery current 2.639 A
IDE01837 Temperature of battery sensor 32 °C
IDE01838 Battery temperature 27 °C
IDE01839 Battery charge level 85 %
IDE01841 Battery internal resistance 6.6 mOhm
IDE01842 Usable battery charge 38 Ah

 

[Benny5]

Lots of data there.
This is the one that stands out for a non-tech like me;
21/10/2025
IDE01834 Battery voltage 12.256 V (Engine Off)

Its not too dissimilar to my reading of 12.17v.

 

[Mottie]

You've had it long enough. Winter's coming. If you change it now and it turns out you are changing it a year or 18 months too early, how much money are you wasting? A tenners worth of battery? How much aggro would it be if it let you down? If you’re happy to gamble a tenner on that, carry on and wait for the inevitable.

 

[Benny5]

Yes, I'm planning on get it changed out in the next few days.

Thanks for all the input.

 

[Johntheo5]

Lots of data there.
This is the one that stands out for a non-tech like me;
21/10/2025
IDE01834 Battery voltage 12.256 V (Engine Off)

Its not too dissimilar to my reading of 12.17v.

Possibly, one of the "best" bit of data above, is, IDE01843 Battery voltage at rest 12.4 V although how they calculate that without a disconnected battery is definitely pure magic! and it does show a IDE01839 Battery charge level 78 %, close to the theoretical numbers, below. Also the
IDE01842 Usable battery charge 38 Ah after the ~ 2.5 years vs the now IDE01842 Usable battery charge 27 Ah is interesting, but, I suppose, since a 3 sec, 300A start only consumes 0.25AH then no worries at even 27AH, the one, IMO, to also watch is the battery internal resistance which drops the battery terminal volts, a 4Vdrop from a nominal 12V to 8V will possibly result in no cranking and requires a battery reasistance of 13.3 mOhms.

12V Battery Voltage	State of Charge
12.70	100%
12.50	90%
12.42	80%
12.32	70%
12.20	60%
12.06	50%
11.90	40%
11.79	30%
11.58	20%
11.31	10%
10.50

 

[Johntheo5]

Yes, I'm planning on get it changed out in the next few days.

Thanks for all the input.

Do you know if your car has this energy saving smart Alternator charging?, if so, then, its very advisable to get the battery coded/adapted.

 

[Benny5]

I’m not absolutely sure but I think it has. Otherwise, I would have changed it out rather than paying Halfords the extra for fitting. I expect they will have the expertise/equipment to change it out seamlessly.