Preconditioning issues - Low battery warning

[Deman77]

Originally Posted by Deman77

Had no issues (happened 3 times in total) over last two winters and last week car gone into stand by after just 3 days idle and when woke up refusing to do preconditioning.

It’s going for failing stop start investigation which works for dealer test after fully charging the batteries but fails for me after spending a couple of days on the drive. I suspect they are related and battery drain is the problem. My stop start has not worked (well a couple of times after 1hr plus journey) since new look software update in summer.

Mine came back. BMS module was giving fault codes. It was interpreting the battery as low charge level and hence preventing stopstart and pre-conditioning. The battery was NOT drained. They updated the module firmware and saying it fixed it. I will report back after a couple of weeks unless it breaks sooner.

I usually precondition mine so engine and gearbox should be at good temperature shortly after driving off. I have no screen heater. So the only thing that can prevent stopstart is -5C outside (subject to sensor tolerances) or low battery temp (whatever that means). In this weather (+2/+4C) I expect it to work and dealer tests yest and today in near zero demonstrate that it works in this weather so no excuses.

[Philip Fisher]

Mine started precon this morning on the timer but then failed about 20mins in citing low battery. As soon as I booted up the car it started the ICE immediately as the 400v battery was indeed completely flat. This leads me to believe that - on the T8 - the precon heater gets it's juice from the 400v battery and not the 12v systems battery in the boot......

[Lexman8]

Originally Posted by Philip Fisher

Mine started precon this morning on the timer but then failed about 20mins in citing low battery. As soon as I booted up the car it started the ICE immediately as the 400v battery was indeed completely flat. This leads me to believe that - on the T8 - the precon heater gets it's juice from the 400v battery and not the 12v systems battery in the boot......

It may have been a coincidence that the precon stopped and the 400v battery was depleted. I assume* the T8 uses the aux heater same as the D5 and T6 and therefore the only components drawing current are the aux heater controller, the water pump, the climate system fan and a few control modules. These would all be 12v components and it would be inefficient to convert 400v to 12v to power them alone, not to mention the complexity of it. Also, the 400v battery is rated at ~9kWh which is about 10 times that of the 12v battery so it could probably run the precon system for hours before it was exhausted.

Is it possible that the 400v battery was exhausted anyway and that the 12v battery was partially depleted leaving only 20 mins of precon use?

*Not having a T8, I'm guessing a bit here.

[Philip Fisher]

I follow your logic but the 400v battery had a smidgen of charge when I parked up and none at all when I started again in the morning. I drove home in hybrid mode and in this mode it will always leave a tiny bit of charge so when you boot the car in the morning you can always get at least 50 yards before the ICE starts.

However this morning there was nothing at all. The ICE started straight on booting the car, which is unheard of. The only way of depleting the battery this much normally is to put it in pure mode and drive with a feather foot until it completely discharges.

So i conclude that the aux heater discharges the 400v system (possibly indirectly) to run the pump and controls. I have also had a long running suspicion that the 400v battery charges the 12v battery through a transformer and they share a common earth, and this supports that theory.

Incidentally we were away in the motorhome a few weeks back and due to a lack of hook up, a lack of sun on the panels and a generally shoddy leisure battery we managed to deplete all our electricity in the evening running the heating and a few lights. This meant that in the morning we had 7.4v left in our battery and no chance of running the heating to take the chill off the minus 1 outside. Now our boiler is admittedly different with a bigger system to pump round and it uses gas rather than unleaded as the heat source but the basic premise is the same and I was surprised how much battery it used for the heating alone. I think it was using 1 to 2 amps just to run the gas heating and would imagine the car could be similar....

[SpaceBoy42]

The 400V battery does charge the 12V battery as I have seen it do it with the ignition switched on. The 12V battery terminal voltage jumps from around 12.5V up to 13.8V when the hybrid battery starts charging the starter battery. It only does it when it thinks it needs to.

It also jumps to 13.8V if the ICE is running. My understanding is there is no alternator on the T8 so the ICE generates electricity using the starter/generator and regulates that down to the 12V to charge the starter battery with a reasonably beefy switch mode power supply.

[Lexman8]

Ah, okay, then it looks like the 12v battery is charged from the 400v side and therefore eliminates the need for a 12v alternator, thus simplifying the 12v side.

[Deman77]

Originally Posted by Deman77

Mine came back. BMS module was giving fault codes. It was interpreting the battery as low charge level and hence preventing stopstart and pre-conditioning. The battery was NOT drained. They updated the module firmware and saying it fixed it. I will report back after a couple of weeks unless it breaks sooner.

I usually precondition mine so engine and gearbox should be at good temperature shortly after driving off. I have no screen heater. So the only thing that can prevent stopstart is -5C outside (subject to sensor tolerances) or low battery temp (whatever that means). In this weather (+2/+4C) I expect it to work and dealer tests yest and today in near zero demonstrate that it works in this weather so no excuses.

Two weeks on and I am back to the same old. Pre conditioning refusing to work when you most need it and stop start would not come on even over long trips - all conditions met. I am pretty sure it’s battery drain and not software. Why else would it get worse after two weeks. Three visits for the same issue and still not fixed. Very frustrating.

[Lexman8]

Does sound like a voltage issue:

• duff battery or batteries
• problem with charge controller
• cut-off voltage set too high for precon and s/s
• battery-state sensor and/or its controller faulty
• other

The problem with these cars is their complexity and therefore the difficulty of finding the actual problem in the absence of sophisticated in-built diagnostics including perhaps real-time monitoring and logging.

The issue with BLIS on my car is still ongoing after nearly 3 months since I first reported it.

[neon]

Not sure which thread to use as about 4 on similiar subject.
I am now getting low battery warning again when trying to use the auxiliary heater.
What a waste of money that very expensive option was when it does not work more often than it does. I would have expected an upgraded battery for those choosing the option to ensure it works more often.
Looks like a call to the dealer.
Trouble is last year when I raised it, progress was so slow that winter was over and no longer an issue.

[Lexman8]

The strange thing is that my precon works 100% of the time even though I tend to do only short journeys plus usually one longer journey per week. Also, sometimes the car is unused for a day or two.

As I posted previously, the only difference may be that I usually keep the car in the garage overnight so it seldom (never really) gets below freezing. Perhaps the problem is a (very) cold battery dropping below the threshold voltage?