[JT Rock]

I can't imagine that I'm the only one experiencing this issue. My 2021 P8 vehicle has v2.3 software and it still abuses the 12v battery if I leave it plugged in after the HV charging session has completed. The issue happens only while the temperature is below ~60°F (it works perfectly normal in warmer temperatures). I've mentioned this problem last season where my voltage logger shows the 12v LV battery being unnecessarily drained. Judging by the logs, it seems to be undergoing periodic handshaking with the EVSE. (I notice that my EVSE will blink during that time) . I use the Grizzl-E classic @ 240V/40A, but it also happens with other EVSE's including the Volvo portable one. Keep in mind that HV charging works perfectly. I just don't like having to remember to unlug immediately after charging has completed in order to extend the life of my LV battery.

I just tested it again last night:

The good news is that eventually, when the LV battery crosses below the 12v threshold, the HV battery will automatically start charging the LV battery. I keep hoping for a software fix for the drain issue, but I'm starting to realize that's not going to happen unless I can prove that others are affected by it. If I can't, then I need to convince Volvo to fix my specific OBC unit.

When I read posts about LV batteries going bad, I can't help but think that maybe the vehicle is causing them to prematurely fail. Example:
Software update question… Owner install or take to...

 

[SwedishC40]

Very interesting. But what could it be doing using the 12V battery while plugged in, and only in colder temps?

Is the X-axis hours? Was it plugged in the whole time the graph shows?

 

[BuzzyBud]

Curious. Do you obtain a different result if you lock the vehicle while it is connected to your level 2 charging device?
The fact you obtain a different result based on ambient temperature would point me in the direction of the winter settings within the climate module. I assume you have examined these settings and turned off all the ones we use during the winter months.

 

[JT Rock]

Very interesting. But what could it be doing using the 12V battery while plugged in, and only in colder temps?

Is the X-axis hours? Was it plugged in the whole time the graph shows?

The X-axis is hours (48 hours = 2 days based on dates shown at the top).

Here's an outline of what transpired within that graph:

 

[JT Rock]

Curious. Do you obtain a different result if you lock the vehicle while it is connected to your level 2 charging device?
The fact you obtain a different result based on ambient temperature would point me in the direction of the winter settings within the climate module. I assume you have examined these settings and turned off all the ones we use during the winter months.

I always lock the vehicle while it's charging. I don't remember if I've ever reviewed the log while unlocked.
While locked, I doubt any climate settings would impact it. I don't have any charging scheduled either.
I'll also add that climate settings don't take effect until 50°F or below, I think. I have a thermometer in my garage, and I know that the issue still occurs in the high 50's.

 

[BuzzyBud]

Sorry about my curiosity! It would seem your 12V battery activity is somehow connected to your HV charging routine. (I am attempting to rule out the level 2 charge station as the source of your problem.) Do you have access to an activity log generated by your level 2 charger? (Attached below is the activity log I use with my ChargePoint Flex.) If you have a log, what does it show?

 

[JT Rock]

I'm not sure what you're getting at. My EVSE is not smart, but I do have a whole house voltage/current/power logger. The HV level 2 charging works perfectly fine. The 12v drain happens after when the charging has completed. My house logger shows no appreciable power (<10W) being drawn by the EVSE at those times. The EVSE blinks like it does while it is initially negotiating a charging session, but no current is actually dawn from the AC line.

 

[BuzzyBud]

I'm not sure I have any additional thoughts which might be helpful. I completed a quick review of known Volvo Service Bulletins as listed for an XC40 2021 which might connect the 12V battery to Diagnostic Trouble Codes during a service visit. Nothing was a hit you could reference during a visit to your service center.

 

[SwedishC40]

Why the dip around the 12 hour mark, looks like it fell to just above 12V while parked at the store🤔

 

[JT Rock]

The dip at the 12hr mark was just me going back to the car and opening it for 10 seconds to get something out. I'm not sure why it dropped lower than usual.

 

[Vollol]

The good news is that eventually, when the LV battery crosses below the 12v threshold, the HV battery will automatically start charging the LV battery.

At 12V the battery is completely drained and getting damaged. It should be floated around 12.65-12.7V (depending on chemistry). So this recovery point seems too low.

I wonder if the car was meant to ship with a Lithium LV battery, and they swapped it out for lead AGM without changing the charge profile?

 

[SwedishC40]

Yeah I was also thinking 12v is way way too low, not good for the battery at all 😕

 

[SwedishC40]

Have you tried doing any measurements while pre-conditioning? Would be interesting to know if that involves the 12V battery, and if it starts charging it immediately while plugged in and pre-conditioning.

 

[JT Rock]

Have you tried doing any measurements while pre-conditioning? Would be interesting to know if that involves the 12V battery, and if it starts charging it immediately while plugged in and pre-conditioning.

When pre-conditioning, the voltage is over 14v, and therefore the LV battery maintainer is engaged. Although, I haven't investigated if there is a scenario possible where seat & steering wheel heaters can be activated without the maintainer engaged. I know that the infotainment computer and screen can run without the maintainer being on.

 

[Bushikatagi]

My anecdotal experience is that I have had my 12v battery die probably 6 times now. I think only once did this happen while the charger was connected though. I had the battery replaced by the dealer about 7-8 months ago and it just died again. This most recent time it has been very cold down to almost 0F but still no excuse for a less than one year old battery.

I do think you are on to there being some kind of software bug causing the 12v battery to drain excessively low though. My theory is that at some point if it doesn't self-correct and start charging soon enough the voltage could sag too low to activate the relays that connect the HV battery to the low voltage charging hardware. Perhaps over time the battery just weakens enough that it is inevitable...