OK so I have 2009 Ford S Max 2.0 TDCI. Titanium

 

I’m an old man I don’t drive a lot anymore so the car sits for long periods of time doing nothing, I must have left something running that drained the battery because one day I went out to the car and the battery was completely flat.

 

I bought a new battery put it in because the car was going for its MOT which it past with no major issues everything is fine for a couple of weeks.

 

Now what’s happening is I get in the car start the engine which starts fine but then in about 8 seconds the ignition/battery light, charge light comes on.

 

I went to ask my local mechanic who was in the process of locking up.  He said there’s nothing immediately springs to mind but check your earth strap, check your leads as if you’ve just replaced the battery then you might have disturbed something, make sure everything is in place take earth strap off clean it up put it back tell me what happens, or bring it  back in, in the morning.

 

I went out to head home but then the car wouldn’t start.  It would spin initially fire up but then just die. Tried this half a dozen times same response so we just left the car off to one side locked her up I went home.

 

The following day I walk along to the garage got in the car turn the ignition on, turn the key engine starts no problem everything’s ticking over fine then about eight seconds later the charge light comes on. which was the problem I took the cart of the mechanic for, he said first available slot is about a weeks time, so have I taken both leads off Clean them Clean the battery terminals Sprayed everything with silicone grease and clamp them back on tight, earth strapped to body removed rubbed with a Copper wire brush, also sprayed with the silicone grease and bolted back in place.

I still have the light coming on eight seconds after starting the engine.

 

I have put an avometer across the battery and it is registering good charge, I’ve started the engine left it running then use the avometer and 13.6 volts seems good to me fairly normal so alternator’s showing it’s working fine the battery’s fine but I still get this eight to 10 seconds after engine starts the engine/Ignition light comes on

 

Anybody any ideas?

 

I have read about a battery management reset, but don’t know whether a 2009 S Max has a battery management system, and if it does what is dancing round the houses reset, I’m still trying to find out.

 

But ideas on engine starts fine but then shows the battery light after about 8 to 10 seconds It still has me baffled.

13.6 volts is way too low. The battery isn't being charged effectively. Needs to be over 14 volts.

Usual fault is the SmartCharge system plug on the alternator. Often the small wires corrode and break around that plug.

19 hours ago, TomsFocus said:

13.6 volts is way too low. The battery isn't being charged effectively. Needs to be over 14 volts.

Usual fault is the SmartCharge system plug on the alternator. Often the small wires corrode and break around that plug.

 

Now that’s worth an investigation, thank you I will check that out. 

In my early days of being around vehicles I was told as a rough rule of thumb 13¼v to 14¼v was to be generally considered a acceptable working alternator.  Although I have seen other people quote a full two volts of range and say 13 to 15 is perfectly acceptable.

 And as the battery is basically new and no auxiliary electricals running I thought 13.6v to be within acceptable range.

 But I do appreciate that maybe more modern technology has possibly changed these numbers a little.

 Thank you.

3 minutes ago, An old man called Neville said:

 

Now that’s worth an investigation, thank you I will check that out. 

In my early days of being around vehicles I was told as a rough rule of thumb 13¼v to 14¼v was to be generally considered a acceptable working alternator.  Although I have seen other people quote a full two volts of range and say 13 to 15 is perfectly acceptable.

 And as the battery is basically new and no auxiliary electricals running I thought 13.6v to be within acceptable range.

 But I do appreciate that maybe more modern technology has possibly changed these numbers a little.

 Thank you.

Fords from around 2000 to 2010 have a SmartCharge system which basically just increases the voltage after startup when the battery is still cold. (Cold batteries accept charge more easily). It's not a variable rate charging system like later cars use, it spends most of the time at 14.4v, only increasing to 15v or more when cold for a short period.

13.6v is the default 'failsafe' value for when the SmartCharge isn't working. That will just about charge the battery enough to keep the car starting, but not enough to keep the battery in good condition long term.

On 3/8/2026 at 1:32 PM, TomsFocus said:

Fords from around 2000 to 2010 have a SmartCharge system which basically just increases the voltage after startup when the battery is still cold. (Cold batteries accept charge more easily). It's not a variable rate charging system like later cars use, it spends most of the time at 14.4v, only increasing to 15v or more when cold for a short period.

13.6v is the default 'failsafe' value for when the SmartCharge isn't working. That will just about charge the battery enough to keep the car starting, but not enough to keep the battery in good condition long term. 

On 3/8/2026 at 1:32 PM, TomsFocus said:

Thank you very much for that excellent information.

 

I did give the alternator output a quick check with an avo meter, I also have a small electronic gadget specifically for battery testing and it near enough confirmed what you’ve just said.  The light display on it showed the alternator peak output light was flickering and the middle light was on to indicate it was actually working but not at peak performance Just as you say.

 

I did take it into my Local mechanic on the way home today and he loosely confirmed what you said, it’s booked in for the end of the month, and yes my local mechanic is really good and as a consequence he is normally stacked for weeks in advance.

 

So you have confirmed what he said or I should say he confirmed what you said.

 

Thank you very much you put my mind at rest.