Focus battery issues

[Elroy Blue]

2011 focus mk3 1.6 petrol. It's shown the occasional 'power steering malfunction' which initially filled us with horror that the electric power steering rack had failed. We are now getting a regular 'low battery' on start up, but the car runs fine.
I initially used a very old multimeter with just a light which illuminated amber. However I've now got a digital one that shows 12.4 V, so that suggests the battery is ok.
Why would we be getting the the indications?

[E-bmw]

You don't say whether 12.4 volts was measured with the engine running or not.

A "12 volt" battery is actually a 12.6 volt battery & while 12.4 might sound good then, just remember this.

For every drop in 0.1 volts the battery is actually around 20% less than fully charged so 12.4 is only around 60% charged.

With the engine running and a good battery, you should get around 14.3 to 14.5 volts at the battery.

With a good and fully charged battery, as soon as you stop the engine you should get over 12.5 volts & possibly up to 12.65 volts.

[Elroy Blue]

That was with the engine stopped. But that's useful information. Thanks

[Mignon]

Depends when you measured the voltage. Immediately after a run it'll be higher than after standing overnight if the battery is failing. Try it just before you first start the car.

[Penelope Stopit]

Mignon said:

Depends when you measured the voltage. Immediately after a run it'll be higher than after standing overnight if the battery is failing. Try it just before you first start the car.

This, get someone to crank the engine over while you measure what the voltage drops to
The battery voltage shouldn't drop below 9.6 volts when cranking

[Penelope Stopit]

E-bmw said:

You don't say whether 12.4 volts was measured with the engine running or not.

A "12 volt" battery is actually a 12.6 volt battery & while 12.4 might sound good then, just remember this.

For every drop in 0.1 volts the battery is actually around 20% less than fully charged so 12.4 is only around 60% charged.

With the engine running and a good battery, you should get around 14.3 to 14.5 volts at the battery.

With a good and fully charged battery, as soon as you stop the engine you should get over 12.5 volts & possibly up to 12.65 volts.

And this, check the voltage when alternator is charging

[Elroy Blue]

That was measured when the car had been stood overnight. Some really useful for a mechanical novice. Cheers

[Mignon]

OE Ford calcium batteries usually last for ever. The one on my Focus lasted for 15 years from 2001 to 2016 including some fairly long periods when it was flat while the car was off road. They need a high charging voltage and with the engine running this should be 14.4v to 14.8v. It can go higher if the battery is flat. Check this first with the rpm at 2000 plus.

It does no harm to get a decent battery charger and stick this on overnight and see what happens. No need to remove the battery from the car, just make sure you put the charger clamps on the right way round. After an overnight charge leave the battery for an hour to stabilise or put the sidelights on for a bit to give it some load. If it's good it should be at 12.65v. As you've been told, small decreases in the voltage mean large losses in its charge holding capacity so even 12.5v is cause for concern.

[Elroy Blue]

With the engine running I'm getting 13.74-13.75v.

I'm going to give the battery a charge and see if that makes any difference before deciding on a new battery

[E-bmw]

Charge the battery FULLY overnight & try the same IMMEDIATELY you start the car.

Either the battery is drawing too much charge & dragging the alternator output down or the alternator is not up to scratch, the above will tell you.

[Mignon]

When my Focus alternator voltage dropped it was a dirty multiplug connection at the back of it. Removal and a quick squirt of WD40 sorted it out.

[northwestrecovery]

I don't think you cant just swap a battery on a focus , i; sure it has a smart charging system and needs programming / coding in .

[Elroy Blue]

Charged the battery up and it was showing 13.09v off and 14.08v running.

[Mignon]

13.1v from the battery is not a genuine voltage. You didn't remove the surface charge from it having just been charged up as I advised above. However the alternator output is low so check the drive belt and connections.