Battery voltage low ?

Sounds well low to me. Maybe the alternator isn't charging it?

mk 1.5 04 1.8 focus petrol

Last week my wife had the RAC come out as she had a flat tyre and was unable to losen 2 of the lugs. She mentioned it took a few goes maybe 2/3 times a months to start it so he did a battery check and it read as 12.48v "good battery" "re-charge"

I've just topped up all the fluids before a long drive today and put a meter across it and its reading as 12.37v is this too low to leave it at. Car starts fine everything is running spot on, although there is more demand with heat/demisters/lights etc.

Should I buy a charger and give it a charge or just try and use less heat/demisters etc and hope it's volts increase after a long drive.

I've not charged a car battery before, do I have to disconnect the +ve and -ve cables before charging it or do I just attach clamps from the charger straight on. Its no big deal to remove the leads a couple of 10mm nuts and I have the radio code.

Out of interest what is the normal voltage for a battery ?

Thanks

It happens that Jeff formulated :

If you are charging with a modern small battery charger, then no need to disconnect it.

What meter are you using to measure the voltage? It may not be that accurate. Can you try it on another car battery to see if it reads a bit low on that one?

With a normal battery charger, there is no need to disconnect the battery. You only need to do that if using a "quick boost" charger, and I would recommend never doing that anyway.

In your position, I would ignore the actual voltage readings. Measure the voltage with the engine off. Start the engine, measure again, and it should have gone up a bit. Switch headlights and heater blower on (with engine running) and it should still be at least as high as with the engine off. If that's what you see, and the car is starting OK, forget it.

Note that the Focus uses Ford's "SmartCharge" system, so voltage readings can sometimes produce unexpected values.

WRT the times when it's slow to start, has that followed a period when the car had been started, run for a short period, then switched off? If so, that may well be the anti-flood system kicking in. If that is the case, hold the pedal to the floor whilst cranking, and it will start.

FWIW, I've had a battery last for 10 years on a Focus, and still start it in the winter, so there may well be plenty of life in yours yet!

Chris

Hi Harry,

It looks to be the priginal motorcraft battery its an 04 so approximately 8 years old which is fairly old as I think they're suppose to last around 5 years or something I think I was told at a garage.

So you think charge it and see how it fairs ?

As I say starts and runs fine, but I have been using a lot more features heat, lights and such like so its bound to have affected the battery. I'm hoping its just that other new battery time.

I'll do some googling on a cheap and effective charger I guess there all much the same and give it a charge.

It depends on the state of charge and when you measure it. The ambient temperature make a difference too.

There is no need to worry about the off load voltage provided it starts ok.

There's no need to disconnect a battery when charging it with any sort of charger likely to be found at home.

In normal use, modern cars never need an external charge.

The power doesn't come from the battery once the engine is running it comes from the alternator.

Hey up Chris

I'm using an auto one I got from maplins som eyears back.

I tested on on a mk4 golf heres the readings:

(has had a 10 minute drive in the last 30 mins)

The focus Now reading 12.31v when off

What do you reckon with the above findings, seems ok ?

Ahhh I see could be an explanation of my readings.

I remember reading about that in the manual. It has happened in those circumstances but also when its not been run in the morning.

Wow I didn't know they could last that long, very impressives! The battery from the golf I tested has been in since the car was pushed off the production line and its a 1999 model. I guess I better no right my battery off just yet :)

Extremely helpful post and thanks. It could be that I am being over cautious here as I had a breakdown on a previous car with a flat battery and was left stranded and the AA took their sweet merry time to come to me.

Hope you can see from those readings how things stand.

I see so you think it could be a fault on the alternator not putting out enough ?

That is a strong possibility but has someone else said if you monitor the voltage with the engine running that should give an indication if it is a battery or charging problem. Voltage should rise to anything up to

I'd be a bit wary of any clip on tester that claims to properly diagnose a car battery.

It would have been a better comparison if you had not switched the HFS on; those things take a *huge* current by automotive standards, and the alternator will never balance that load. (With just headlights and blower on, you should see somewhat more than 12.31v; that would confirm alternator is most likely OK.)

Keeping that in mind, it would appear to me that your battery and alternator are fine. If you are determined to replace the battery on grounds of reliability, make sure you get a proper silver technology one that modern Fords require, or you may make things worse! Bosch are highly regarded by most in the know.

Yep.

Modern cars start so easily, and charging systems are so much better than old cars, that by the time a battery is slow to start a car, it's often dead. The other thing that can happen, although rarely these days, is failure of a cell-to-cell connection. No amount of testing will identify that, and it *could* happen at any time in a vehicle's life, so there is no realistic way of ensuring absolutely that a dead battery won't strand you.

Yep; unless you are determined to spend some money, just use it ;-)

Chris

That is a strong possibility but has someone else said if you monitor the voltage with the engine running that should give an indication if it is a battery or charging problem. Voltage should rise to anything up to

I'd be a bit wary of any clip on tester that claims to properly diagnose a car battery.

I've got a chart around here (somewhere) which is used after a sealed battery has been charged and left for two hours which give a good indication of the battery condition from the voltage read.

That would be fine for you or me, but I would suggest that the OP gets a new battery asap. It's lasted 8 years already, well above the norm,and I reckon the next frosty morning will do for it.

The OP's posts tells us that he's not exactly well versed in DIY mechanicking, and the car is used by his wife, who's already had the RAC out to a flat tyre. Continuing with this battery is tempting providence IMHO.

Steve

There are electronic testers around these days which do a short high current pulse test and compute the battery's true capacity in amp.hr. The correct amp.hr of the battery should be marked on it, and if the test shows it to be less than 65% of the nominal amount, it's time to replace it.

A simple voltage test won't show up one of the most common failure modes, where one or more of the cells go high impedance and can't deliver the high current needed to start the car anymore.

When I posted here a couple of years ago that I had changed the battery on my Focus at 10 years old, although it was still starting OK, I was surprised that many folk were getting 10 years plus from their batteries these days.

In the OP's position, I would be more inclined to spend my time and money investigating why the car "takes a few goes" to start sometimes...

Chris

My old 05 plate Puggy still has the original battery and starts fine even in frost.

Chris

Not from those numbers.

I changed the battery on the SD1 a few weeks ago, and that was just over

Indeed. I'm too mean to change an expensive item like a battery 'just in case'