MINI One - 11.9V should be enough to start a car? - JonathanDS

Heya - my Mini One no longer starts, it just makes a clicking noise on turning the key.

I was hoping that it's just a dead battery - it is 10 years old after all - but testing with a multimeter shows it's still at 11.9V. That's a little low, but that should be enough to get the car started, right?

Just wanted to rule out the easy options before I have to call a mechanic out.

MINI One - 11.9V should be enough to start a car? - Falkirk Bairn

If it's a manual,12v & a bump start is the first thing to try.

You cannot bump start an auto.

Bump start - ignition on, car in 2nd/3rd gear, clutch pedal down.

Get a push from willing helpers - when the car is moving at greater than walking pace bring the clutch up - with a bit of luck it will start.

MINI One - 11.9V should be enough to start a car? - elekie&a/c doctor
Voltage is not an indication of a good battery . A flat battery can show 12 volts , but not be good enough to start a car . At 10 years old , it’s time for a replacement. Just be careful to get the right one . If the car has stop/start , you’ll need the correct type .
MINI One - 11.9V should be enough to start a car? - Railroad.

11.9v indicates the battery is completely discharged. Anything under 12.2v means the battery is in a state of discharge, and a healthy battery should show 12.6v in a static state. Yours needs to be replaced.

MINI One - 11.9V should be enough to start a car? - thunderbird

11.9v indicates the battery is completely discharged. Anything under 12.2v means the battery is in a state of discharge, and a healthy battery should show 12.6v in a static state. Yours needs to be replaced.

I fell into the "its showing 12.3 volts so must be OK" club some years ago before I was educated and shown that at 12.3 volts its unlikely to start the car. Standing voltage is not the beat indicator of battery condition but its the one available to anyone with a multimeter.

When my car failed to start with 12.3 volts on the advice of the local factors I bought a new battery and my problem was solved and never happened again. The battery in question was the original and was 7 years old, a replacement of the correct type for a Focus petrol was just over £50 and was still going strong when the car was 12 years old and sold. I checked the voltage once a blue moon first thing in the morning and it was still showing 12.7 volts.

How many of us actually realise a 12 volt battery is not actually 12 volts. The battery has 6 cells each of 2.1 volts making a fully charged battery 12.6 volts. I presume my multimeter was a bit out when it showed 12.7 volts after standing overnight.

MINI One - 11.9V should be enough to start a car? - Railroad.

We also might refer to a battery as being knackered, or whatever. But in scientific terms like anything else there is one of many things that might be wrong with a battery, and all will produce different symptoms. a battery tester cannot understand the term 'knackered', but they will carry out a particular test depending on the type of tester.

I was taught a lot about batteries and battery faults when I was an AA Patrol, especially considering battery related problems are one of the biggest reasons people use breakdown services.

Firstly the engine starting or otherwise is not conclusive proof of battery condition. There's a lot more to it than that. But a very good reliable test is as follows.

With a cold engine, and first thing in the morning measure the battery voltage. If it reads 12.6v there's a good chance it's healthy. When the engine is running the battery voltage will be around 14.4v. This builds up a surface charge on the battery which must be removed before testing. You will not get an accurate diagnosis if it isn't. If the engine has run switch on the headlamps for about 20 seconds to take the surface charge off, then carry out the following test.

You will need to prevent the engine from starting by pulling the ECM fuse or something like that. Then connect a voltmeter across the battery and crank the engine for a minimum of 10 seconds. Observe the battery voltage whilst cranking and a petrol engine must maintain at least 10v for that cranking period. A diesel must maintain 9.5v for that time. When you stop cranking the voltage should return to around 12.6v after a short while. Crucially during cranking the voltage change between the start and the end of cranking must not be less than 0.3v, eg if it starts at 10.5v it must not fall lower than 10.2v while your cranking for 10 seconds. If it does the battery needs replacing.

If it doesn't it's the best indication you can get that the battery is in good condition.

MINI One - 11.9V should be enough to start a car? - JonathanDS

Thanks for the advice all - sounds like it's well past time to get a new battery, I'll start with that.

MINI One - 11.9V should be enough to start a car? - Cris_on_the_gas

Thanks for the advice all - sounds like it's well past time to get a new battery, I'll start with that.

You might be wasting your money

Measuring the voltage of battery under no load is not the whole story. The important thing about batteries is not the voltage but the internal resistance. Now if you have an ohmmeter don't try to measure this. If you try then you are putting a full short across the battery which is very dangerous.

A good battery will have a very low internal resistance so whatever load is applied across it the voltage across the load will be much greater then the voltage across the internal resistance of the battery. In a car the starter motor is by far the biggest load you can apply. So when starting the car almost 12V will be applied to the starter with a good battery. with a bad battery this will be much lower. Generally if battery voltage drops below 10V when cranking then battery either needs to be charged or replaced if it won't take charge. So you could try once you get car started by either jump starting or charging the battery with a battery charger for at least 8 hours. Measure the voltage when actually trying to start the car

If you don't fancy this then you could get a battery tester. This measures the internal resistance of the battery by placing it under a known load and the meter is a voltmeter with red, yellow or green calibration marks to show the condition of the battery. Just seen a battery and alternator tester on Google search for £15. Might be worth buying, cheaper then a new battery. Last time I had battery issues local auto factor tested it for free, I think most places should do this.

MINI One - 11.9V should be enough to start a car? - Andrew-T

If there's no reason to believe the battery to have been discharged by lights being left on (for example) why not just try a jump-start from a second vehicle, if you have jump leads ? If that works, question answered. But I guess 11.9v is all you need to know.

MINI One - 11.9V should be enough to start a car? - medview

Checkoput your interior light when you try to crank the car. The light should continue to illuminate during cranking. If there's insufficient capacity in the battery and the car won't crank the chances are that the interior light will dim to almost nothing.

This indicates a battery problem unless of course the battery connections are badly corroded.

Joe

MINI One - 11.9V should be enough to start a car? - JonathanDS
Took a while from ordering a replacement battery, and then the battery terminal bolt sheared off when screwing it back in (grr) , but just confirming that a fresh battery has fixed it. Thanks all

Edited by JonathanDS on 16/05/2020 at 12:13

 

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