Odd battery light behaviour..

[wafter]

Early into my trip to work on Wednesday I noticed the battery light was on.

The car had started fine and got me to work OK; at lunctime I checked the battery voltage (ignition off) at IIRC 10.3v, then the alternator output (engine running at c. 2k revs) at around 14v - suggesting the battery was dead / failing to charge but the alternator is OK... this figures as the battery came with the car and is an unknown quantity, while the alternator was replaced a few years ago.

I've ordered a new battery (the delivery of which is now two days late) however I've had cause to use the car since and it's been fine; with no battery light or other problems. I did wonder if Wednesday's problems were the result of a cold start on a dying battery as the other journeys were the return home later that day and a trip mid-morning today.

The little optical electrolyte thing in the battery suggests it's still good, but there was clearly a problem with it on Wednesday given its output voltage. I did wonder if it was time related, however the car was used on Tuesday but then stood for several days between Wed and today; I'd have thought if the battery was slow-discharging over time I'd have seen a greater problem today.

I did consider that it might be a dodgy connection somewhere; I tweaked the terminals and checked they're done up properly. Can anyone please suggest any other potential causes of this behaviour?

Ta

 

[sleuthey]

It sounds like the battery has reached the end of it's useful life as I would expect a healthy battery to read more than 10v after a typical drive to work. It sounds like there was just enough Ah to start the car on each occasion. When the voltage goes below 10v then the solenoid starts to reciprocate and lower still a single click and lower still no noises at all.

The warning light has served its intended purpose and warned you in advance of complete failure allowing you to order a new one.

 

[wafter]

It sounds like the battery has reached the end of it's useful life as I would expect a healthy battery to read more than 10v after a typical drive to work. It sounds like there was just enough Ah to start the car on each occasion. When the voltage goes below 10v then the solenoid starts to reciprocate and lower still a single click and lower still no noises at all.

The warning light has served its intended purpose and warned you in advance of complete failure allowing you to order a new one.

Thanks - I was thinking similar; was juat a bit perplexed as to why the light evidently went away.. hopefully the replacement will turn up tomorrow and the light will come on again just to confirm that I'm not binning a battery with some life left in it!

 

[CXRAndy]

If you have a DC clamp, you can see how much current the battery is accepting. A low current would suggest a dead cell.

A low charged battery would taking many tens of Amps. 30-70A

 

[wafter]

If you have a DC clamp, you can see how much current the battery is accepting. A low current would suggest a dead cell.

A low charged battery would taking many tens of Amps. 30-70A

Thanks - didn't know what that was but googled it and I think my gaffer's swanky unit has that functionality so I'll try to pique his interest tomorrow

I'm guessing it measures current draw through induction in the clamp....?

 

[Wobblers]

A fully charged battery will read more than 12.6V: anything below 12V indicates it's flat. Given that your battery was 10,3V but was still able to supply enough current to start your car, I'd suspect a dead cell, so the remaining cells are doing all the work. That would also explain why the electrolyte indicator still shows as good, as it only measures the electrolyte in one cell, which is still okay. The remaining cells are likely also close to end of life. Best to replace it sooner rather than later, as doubtless it'll fail completely at the worst possible time!

PS: A DC clamp meter works by measuring the magnetic field generated by the current.

 

[oldwheels]

I have an intermittent battery flashing warning when ignition is first switched on but vanishes when engine starts. New battery fitted as it failed to start due I suspected to the battery being pretty old.
This appears to be eco mode indication but so far I have no reasonable explanation for this behaviour. Peuguot Partner TDI 1.6.

 

[CXRAndy]

I'm guessing it measures current draw through induction in the clamp....?

Yes.

Because car batteries have quite a lot of current for starting and charging, you can really only measure this with a clamp around a cable.

Most modern digital meters only go up to 10A in series current measure connection, but with a clamp you can measure (model dependant) up to 1000A and more.

The other method is to use a shunt but is a faff compared to a clamp.

 

[wafter]

Thanks guys - every day's a school day and I appreciate the help as I'm far from savvy with electrics!

Thankfully the car started perfectly this morning (in probably the lowest temperature since this started) and got me to work fine. I've just checked the voltage at 12.8v with the engine off; which going on what I've been told / what little I know appears low - IIRC typically car batteries operate at around 12.7-14v..? I'd guess that after a decent 20 mile run it should have more charge in it that that..

I tend to agree with the suggestions so far that it's on its way out; it's just a bit odd that the problem seemed much worse last week and now *appears* to have gone away..

 

[wafter]

Tested again this morning post-work-arrival at 13.1v. Replacement battery has finally arrived, four days after it was supposed to. I'm keeping it in the car and will swap it over when the other one dies / I can be bothered as I know they have a finite shelf life..