Car Battery

forgotmyname

11v with the engine off?  My car will not start with a battery that low.  At 12.2v it's going to be slow and cross your
fingers, start praying and touch wood time.

Don't forget a battery with no load will not give an accurate reading.  Not sure if it was here or elsewhere but they said their
battery was fine about 12.4v.  They switched their lights on and tested the voltage and it dropped to around 9v so the battery
was in fact in a bad state.

sevenhills

forgotmyname said:

My car will not start with a battery that low.  At 12.2v it's going to be slow and cross your
fingers, start praying and touch wood time.
Don't forget a battery with no load will not give an accurate reading.  Not sure if it was here or elsewhere but they said their battery was fine about 12.4v.  They switched their lights on and tested the voltage and it dropped to around 9v so the battery was in fact in a bad state.

Yes, the voltage on my reader lowers when I switch the ignition on, then comes back up, but being around 12.2v is not uncommon, it starts easily.

I have just tested my battery after it was charged a few days ago, 12.6v; the battery that I removed in June read 12.4v after being charged.

Goudy

It's not volts that start the engine, it's amps.

This is a 12v battery, 
RS PRO Alkaline 12V, A27 Battery | RS (rs-online.com)
But there is no way it will start an engine as it is only producing 0.25 amp.

This is another 12v battery,
Varta BLUE Dynamic D43 12Volt 60Ah 540A/EN 560 127 054 3132 car battery | Lead-Acid Batteries | Batteries by Type | Battery Group
This will start the engine as it's 60 amp hours.

It also has a another rating, the CCA or Cold Cranking Amps.
This is the batteries ability to sustain a high load when cold for a certain length of time.
The CCA is generally around 9 times or more the battery's normal amp rating for a decent car battery.

The figure relates to the number of amps it can deliver for 30 seconds while maintaining a voltage of at least 7.3 volts at a set temperature.

As written before, it's quite possible for a car battery to test around 12 volts or more but it's ability to produce amps could be limited due to age/use.

A car battery is made up of interconnected cells, so 6 cells at around 2 volts each produces 12v.
If each cell can hold around 10 amps each, it's a 12v 60 amp battery.
If one cell is completely buggered, it can no longer produce 12 volts or 60 amps.
It's more like 10v and 50 amps (though it's likely much worse as the dead cell will leach from the other cells)

If all cells are holding 2 volts each but perhaps the plates in those cells have started to sulphur up, you can no longer draw the current (amps) from those cells, so the amps drop but  the volts might stay the same, until it's put under load.

So if it can only pull 5 amps from each cell, that's 12v 30amps.
30x9 is only around 270 CCAs.

An average small to mid sized engine cars starter motor require something like 400 amps at around 12 volts to start a cold engine, but for only a short burst (hopefully).

Obviously the CCA test and the conditions to start your car on a frosty morning aren't the same thing, it could take more, for longer or repeatedly, so when the amps in a battery start to drop off, it doesn't take much to make them useless to start the engine but it could still have enough volts and amps to run the rest of the cars electrics as they need nowhere near the same amps to run.

It's usefully to test a battery's voltage and the voltage the alternator puts out, but it is not a conclusive test of the battery's condition.
It's ability to have high amps drawn from it when cold is what's important to start the engine, hence the drop/load test.

forgotmyname

sevenhills said:

Yes, the voltage on my reader lowers when I switch the ignition on, then comes back up, but being around 12.2v is not uncommon, it starts easily.

I have just tested my battery after it was charged a few days ago, 12.6v; the battery that I removed in June read 12.4v after being charged.

Dropping with just the ignition and no other load?   Or is it a diesel and its pulling 60amps of glowplugs etc?

So what happens when you leave your headlights on for 15 minutes?  With the lights and igntition still on what does the voltage show?

As the post above shows the A27 battery is 12v but stick a headlight on that and the voltage will plummet to almost nothing because
it cannot supply enough power.

12.2v to me is very low, cold frosty morning my battery shows 12.86v.  Headlights/hazards/heater blower on and it drops to 12.82.
10 minutes later and its still at 12.76.

sevenhills

forgotmyname said:

Dropping with just the ignition and no other load?   Or is it a diesel and its pulling 60amps of glowplugs etc?

It is a diesel, so that must be why the voltage drops. When it's running the voltage increases up to 14v, but can drop down to 13v with lights/fan on etc. So the alternator is charging, but should it be outputting more?

Do alternators decline gradually or just stop working?

forgotmyname

If it runs at 14+ volts and drops under load then the alternator is not coping. Thay maybe normal for some cars as long as it
stays above 13.8v. It's still charging at that.

If it drops below that then something needs checking, duff battery bringing the voltage down or a weak alternator.

Goudy

I was reading up on Zafira and it appears the volts out of the alternator read at the battery seem to be a bit lower than some cars.
13.8 to 14.2 volts seems to be the norm.

And yes as it's a diesel, turning on the ignition will cause it to fire up the glowplugs.
These will have a large power drain on the battery.

You could try checking the earth terminals to the body.
The one from the battery should be easy to access, it's probably bolted to the inner wing near the battery.
The one from the engine to the body not so easy.

Other than that if the battery isn't coping, it's either the battery is getting past it (or wasn't great to start with) there's a parasitic drain on it or more realistically it's not recovering from the repeated short tripping.

Your battery is going through hell to start a diesel.
Firing up the glowplugs, activating the starter that is trying to spin up an engine with much higher compression than a petrol engine.
Then you run the car for a short trip, turn it off and do it all again!

Now it's cold, a battery's performance drops away with low temps anyway, the engine is harder to spin up colder as the oil is colder and the diesel in the pump is colder and thicker.
 
I see you wrote it was a new battery, how old is it?

Is it the right one?
Someone brought a car to me last winter with battery trouble. They had fitted a new one from Halfords but the Halfords listing was wrong.
It turned out they were listing one battery for all models based on the battery from an 1980's model car.
What they fitted was only something like 30 odd amps when it needed 50+.
The smaller amp battery just couldn't cope with the EPAS which has a large power draw so the battery just kept draining.

. 

Robbo66

fatbelly said:

I'd give it a charge and see if it behaves normally.

How old is the battery? Six years or more, and you might as well change it.

I wouldn't use Halfords though

I used halfords for my last battery, car died on me and after jumping it I limped to the closed place that sold batteries and this happened to be a Halfords. paid for new battery and fitting and when I sold the car both battery and car were still going strong.

CliveOfIndia

Robbo66 said:

fatbelly said:

I'd give it a charge and see if it behaves normally.

How old is the battery? Six years or more, and you might as well change it.

I wouldn't use Halfords though

I used halfords for my last battery, car died on me and after jumping it I limped to the closed place that sold batteries and this happened to be a Halfords. paid for new battery and fitting and when I sold the car both battery and car were still going strong.

I don't think there's anything wrong with Halfords as such, they just tend to be pretty expensive.  Yes, there's no denying they have convenient locations and convenient opening hours, but I think you pay for that convenience in the price of their goods and fitting charges.

Personally I've always bought my batteries online and fitted them myself.  Admittedly that can be a bit of a fiddle with modern cars that have start/stop and what-not, but for older "simpler" cars it's an absolute doddle to change the battery yourself.  Just put a new battery on my daughter's Micra yesterday, as it happens, took me all of 10 minutes.

People do tend to slag off Halfords a bit, and for some things I can understand it.  I suspect their "mechanics" are more "technicians" who are perfectly capable of doing routine stuff like bulbs, wipers, batteries, etc., but I'd trust my local old-school mechanic a lot more for anything that requires genuine mechanical know-how and experience.

So yep - Halfords are not all bad, far from it, just expensive in my experience.

HillStreetBlues

CliveOfIndia said:

Robbo66 said:

fatbelly said:

I'd give it a charge and see if it behaves normally.

How old is the battery? Six years or more, and you might as well change it.

I wouldn't use Halfords though

I used halfords for my last battery, car died on me and after jumping it I limped to the closed place that sold batteries and this happened to be a Halfords. paid for new battery and fitting and when I sold the car both battery and car were still going strong.

I don't think there's anything wrong with Halfords as such, they just tend to be pretty expensive.  Yes, there's no denying they have convenient locations and convenient opening hours, but I think you pay for that convenience in the price of their goods and fitting charges.

Personally I've always bought my batteries online and fitted them myself.  Admittedly that can be a bit of a fiddle with modern cars that have start/stop and what-not, but for older "simpler" cars it's an absolute doddle to change the battery yourself.  Just put a new battery on my daughter's Micra yesterday, as it happens, took me all of 10 minutes.

People do tend to slag off Halfords a bit, and for some things I can understand it.  I suspect their "mechanics" are more "technicians" who are perfectly capable of doing routine stuff like bulbs, wipers, batteries, etc., but I'd trust my local old-school mechanic a lot more for anything that requires genuine mechanical know-how and experience.

So yep - Halfords are not all bad, far from it, just expensive in my experience.

I have an older car and bought this one https://www.halfords.com/motoring/batteries/car-batteries/halfords-hb063-lead-acid-12v-car-battery-3-year-guarantee-950295.html for £41 delivered.  Fitting was simple even for me.
Wouldn't have though at that price I've been ripped off.