Battery voltage query

[Bolin]

I've had my car on T4 twice - May 2012 and Feb 2013. Both times it said that the battery voltage was low.

Using the OBD, it typically shows 139/140 (13.9v/14.0v) when idling and 14.0v/14.1v when driving along - so appears to be charging ok. When cranking, it did not get below 9v, but the car has always takened a moment to start, never 'instant'.

Can anybody tell me what voltages a healthy battery of the correct spec would show when:

a) car unlocked, everything off, doors/bonnet opened a moment ago, tested with a multimeter (i.e. typical test conditions!)

b) ignition on at pos. 1, nothing else on, looking at the OBD

I'd reckon they'd be expected to be about the same but I'm not an expert with anything electrical

Any help greatly appreciated

[Undercover]

Originally Posted by Bolin

I've had my car on T4 twice - May 2012 and Feb 2013. Both times it said that the battery voltage was low.

Using the OBD, it typically shows 139/140 (13.9v/14.0v) when idling and 14.0v/14.1v when driving along - so appears to be charging ok. When cranking, it did not get below 9v, but the car has always takened a moment to start, never 'instant'.

Can anybody tell me what voltages a healthy battery of the correct spec would show when:

a) car unlocked, everything off, doors/bonnet opened a moment ago, tested with a multimeter (i.e. typical test conditions!)

b) ignition on at pos. 1, nothing else on, looking at the OBD

I'd reckon they'd be expected to be about the same but I'm not an expert with anything electrical

Any help greatly appreciated

A 12v battery is made up of six 2.1 volt cells, so a healthy battery should be 12.6 volts. The reserve capacity, i.e cold cranking should be sufficiently high to prevent excessive voltage drop when the starter motor is engaged. I would say 9 volts indicates a battery is below its best, 9.6 volts or above is an OK battery - remember operating temperatures have an effect on battery volts.

Battery volts on their own isn't an indicator of how good a battery is; volts under heavy discharge is the real indicator.

[FrenchMike]

Originally Posted by Bolin

I've had my car on T4 twice - May 2012 and Feb 2013. Both times it said that the battery voltage was low.

Using the OBD, it typically shows 139/140 (13.9v/14.0v) when idling and 14.0v/14.1v when driving along - so appears to be charging ok. When cranking, it did not get below 9v, but the car has always takened a moment to start, never 'instant'.

Can anybody tell me what voltages a healthy battery of the correct spec would show when:

a) car unlocked, everything off, doors/bonnet opened a moment ago, tested with a multimeter (i.e. typical test conditions!)

b) ignition on at pos. 1, nothing else on, looking at the OBD

I'd reckon they'd be expected to be about the same but I'm not an expert with anything electrical

Any help greatly appreciated

Here it is:

Bat Volt.jpg

Mike

[Undercover]

Originally Posted by FrenchMike

Here it is:

Attachment 22675

Mike

This table gives you the charge state for a battery 'at rest' i.e no current being drawn. Voltage will always drop when a heavy demand is placed upon it. The 'at rest' figures don't give an indication as to a batteries ability to deliver the amps needed to start a car. The only way to test a car battery is through a heavy discharge test using one of these.

http://www.ebay.co.uk/itm/Durite-Dis...#ht_1525wt_721

[FrenchMike]

Totally agree with you and monitoring the voltage during cranking is a good
indication too.

[Bolin]

Thanks guys, I've just got in so will measure i in a couple of hours. When cranking it dropped to 9.something volts, so will measure then start and see what it exactly drops down to.

[crashmarks]

Originally Posted by Bolin

I've had my car on T4 twice - May 2012 and Feb 2013. Both times it said that the battery voltage was low.

Using the OBD, it typically shows 139/140 (13.9v/14.0v) when idling and 14.0v/14.1v when driving along - so appears to be charging ok. When cranking, it did not get below 9v, but the car has always takened a moment to start, never 'instant'.

Can anybody tell me what voltages a healthy battery of the correct spec would show when:

a) car unlocked, everything off, doors/bonnet opened a moment ago, tested with a multimeter (i.e. typical test conditions!)

b) ignition on at pos. 1, nothing else on, looking at the OBD

I'd reckon they'd be expected to be about the same but I'm not an expert with anything electrical

Any help greatly appreciated

I think the T4 is telling you "low volage" because at the time its testing it, it is low. At dle and whilst driving, assuming it was reasonably well charged to start with and you havent got every thing switched on i.e headlights , hated rear screen etc, it should be 14.4v or very close to that. So I would say that its not charging correctly or the battery has an internal fault or there is some other power drain problem although I think the latter is unlikely. What the other guys are saying is right regarding a resting battery and engine crank voltages but it seems to me that isnt what the T4 is testng. You can see from French Mikes table how just a small amount of reduced voltage makes a big difference to the state of charge. My suggestion if its causing you problems or anxiety, would be to test the battery voltage directly accross the battery with a good volt meter, after a few mile run with the engine idling. If its not 14.4 I would try a sustitute battery for another and if the results are the same its probbably a defect within the alternator which may or may not get worse. Unless they have changed design the charge warning light is only connected to one of the 3 phases so yu can loose a phase without the light coming on.

[galaxyclass]

Originally Posted by Bolin

I've had my car on T4 twice - May 2012 and Feb 2013. Both times it said that the battery voltage was low.

Using the OBD, it typically shows 139/140 (13.9v/14.0v) when idling and 14.0v/14.1v when driving along - so appears to be charging ok. When cranking, it did not get below 9v, but the car has always takened a moment to start, never 'instant'.

Can anybody tell me what voltages a healthy battery of the correct spec would show when:

a) car unlocked, everything off, doors/bonnet opened a moment ago, tested with a multimeter (i.e. typical test conditions!)

b) ignition on at pos. 1, nothing else on, looking at the OBD

I'd reckon they'd be expected to be about the same but I'm not an expert with anything electrical

Any help greatly appreciated

Hi, just been out in mine and I get the same readings as you according the to the ipk.

Ignition on 12.9v
Cranking 9v
Running 14.1v

Had no problems with mine however I only use it at weekends.

[Bolin]

Many thanks for the replies guys

I did the test earlier today (and wrote this post, only for the power t go offer just before pressing 'submit' - ugh).

I left the car for and hour and a half without anything electrical being touched at all - I even left the bonnet on the latch so not to disturb the switch and wake the BCU. My multimeter read 12.05v - however, I had done a return trip of just one mile in the morning and soon after turned the engine on for less than 30 seconds to check the fan so I'm not surprised it wasn't fully charged.

I opened the driver's door and turned the ignition to position 1 - the OBD read 11.3v, however, my multimeter read 11.73v.

During cranking my multimeter reading fell to 10.35v I'd previously seen the OBD read 9.somethingv.

Running at idle, OBD read 13.8v/13.9v, multimeter read 14.22v.

So I don't think there is anything too badly amiss, perhaps it's not in the best of health but seems good enough

Odd that the OBD reads lower than the mulimeter - I had checked my voltmeter against thre others recently, so I'm sure it's correct. Perhaps there is a corroded terminal between the battery and the IPK causing the reading to be reduced?

[SD1too]

Originally Posted by Bolin

I opened the driver's door and turned the ignition to position 1 - the OBD read 11.3v, however, my multimeter read 11.73v.

During cranking my multimeter reading fell to 10.35v I'd previously seen the OBD read 9.somethingv.

In your shoes I wouldn't be too happy with some of those figures. The load presented to the battery with just the ignition turned on shouldn't be particularly high, yet your voltage is falling quite significantly.

If you habitually go for trips of one mile and start the engine for just 30 seconds, then I suspect that your battery is protesting and needs a 24 hour external charge.

But Colin; you're original complaint is that your engine "takes a moment" to start. Can you define this in terms of seconds of cranking? And has this battery been on the car throughout the winter months? If so, did it fail to turn over the engine when the ambient temperature was close to freezing?

Simon