Ford Focus ST '22 Battery Drain!

[RaduF86]

Back with updates; I hooked up the charger, and Forscan and I could see the SOC increasing as I wanted to make sure the BMS does in fact detect that the battery is being charged.

Powered of Forscan and left the battery to charge. About three hours later the charger showed the charging has finished and the battery as being Ok. So it switched to trickle charging. I measured the current and it was about 80 mA flowing in the battery. I measured voltage and the charger was "trickling" at about 12.7 V. I did not wakeup the car again to check the SOC at this point.

So my next thought was that something is for sure wrong. I have used the same charger on other discharged batteries and it took at least 10 hours to recharge those batteries.

I left it over night, and this morning the voltage was around 12.5 V. Hooked up forscan, and SOC only 30%. So this idea did not work as I expected.

I have four options left as far as I can tell:

1. Go to a garage to get a battery test and buy a new battery (if test results are bad), reset BMS (sets me back about 200+ euros I guess)

2. Disconnect battery and upon reconnection maybe things get better. 

3. Reset BMS and see what happens. If SOC drops fast -> buy new battery.

4. I have an 8-9 hour trip coming in two weeks. Wait until then and see if somehow the SOC increases during this trip. If not, buy a new battery.

One correction I should make regarding the deep sleep current draw. It is about 35 mA, not 50 mA. Turns out I had to read the clamp meter manual to properly zero it 😄

 

Thank you all for your inputs.

[Tizer]

8 minutes ago, RaduF86 said:

2. Disconnect battery and upon reconnection maybe things get better.

This option will cost you nothing but from what you say I think you need a new battery.

 

8 minutes ago, RaduF86 said:

I should make regarding the deep sleep current draw. It is about 35 mA,

That is good for these cars, 50 mA is the maximum allowed.

[RaduF86]

Yes, in the back of my head I am quite convinced I need a new battery. I am just consciously trying to avoid the unavoidable.

The good point in all of this is that I have learnt quite a few new things.

[Tizer]

40 minutes ago, RaduF86 said:

Yes, in the back of my head I am quite convinced I need a new battery. I am just consciously trying to avoid the unavoidable.

The good point in all of this is that I have learnt quite a few new things.

And the first sign of madness is repeating the same mistake over and over again 😁

[Stevie H79]

So I got myself a trickle charger. Where is the best earthing point under the bonnet. 

[alexp999]

8 minutes ago, Stevie H79 said:

So I got myself a trickle charger. Where is the best earthing point under the bonnet. 

There is a nice "stud" coming out of the body that the front suspension top mount fixes to, that is designed for this purpose. Just to the right of the battery that a big thick cable connects to, it's the main chassis ground point.

[RaduF86]

One final update from my battery analysis/issue.

I disconnector the battery and also removed it from the car. Turns out for the Focus mk4 mhev the only way to remove the battery is to remove the airbox as well. The battery slides inside its tray and it cannot be lifted (this is a really bad design in my opinion).

Anyways, I got it removed, recharged it, and left it in open circuit to let the voltage stabilize for some hours. Then I hooked up one of those cheap battery testers (the BM550 which got quite a few good reviews when compared to more expensive Bosch testers, but apparently the battery must be charged for it to be accurate) and it showed:

- Battery internal resistance 3.86 mOhm

- Battery State-of-Health 91% 

I am not taking these results as 100% accurate, especially the SOH which is only an estimation, but the internal resistance seems low enough for the battery to still be in good shape.

I reinstalled and reconnected the battery, locked the car and left it over night.

Next morning everything worked well, AC is back on, loud beeps, and no more battery saver message on the Synch 3 display. After a few short trips during the morning I connected forscan and the BMS/BCM recalibrated at 70% SOC. Seems a little low, but it is what it is for now. By the way, each test the brake-by-wire unit does after engine turn off draws around 6-7 amps, and that thing does quite a few tests before the car goes to sleep. Of course other ecus are awake also during this time, but the brake one seems to be a particularly high consumer.

 

Conclusions:

Indeed disconnecting and reconnecting the battery does force the BCM to do a recalibration of the SOC. SO thank you for this tip!

I will further keep an eye on it, and if the cheap battery tester shall be proven wrong, I shall order a Yuasa YBX 7096. I saw it is recommeded around the forum.

Since this is the first time the car no longer complains, I also disabled the Connected services to the FordPass app, and the keyless entry. When I shall find some more time to properly diagnose if these cause any unwanted high current drain which might cause the car to go in deep sleep mode again, I am leaving them off.

 

Thank you all for you help!